Wars never happen, when forces, alliances and intentions are known in advance. In those cases, the weaker party simply yields to the demands of the stronger. Every war is preceded by misunderstanding. That is, the different sides live in different perceived realities. The expectations on both sides are typically completely out of whack. I will going to try to shed some light on these expectations and if you think that they are ridiculous, that's precisely what makes them dangerous. Also, I should state up front that because of that, these events are quite unlikely and the probability of a large-scale war is fairly low in normal terms, but uncomfortably high in terms of the potential damage it can cause.
First statement that you can verify by talking to any Armenian you can find: the overwhelming majority of Armenians is crazy. Not just the government, not just the political class, not just the intelligentsia, not just the population of the country, but near-everybody for whom their Armenian heritage is part of identity, both inside and outside of Armenia, including the entire vast Armenian diaspora around the world. Of course, there is a large absolute number of perfectly sane Armenians, but they are a tiny minority with zero political clout. The rest is perfectly capable of enormous sacrifices for their nation, which they perceive to be existentially threatened. They are, on average, much crazier than Israelis even.
Azerbaijanis are only slightly less crazy. While they do not feel existentially threatened, the refugees from Nagorno-Karabakh and Agdam county as well as the humiliated military establishment thirsts revenge. Politicians of all stripes have vowed to retake Karabakh in the very near future.
Both Armenia and Azerbaijan spent around 3%-4% of GDP on Military, with a steep hike in the past two years in both countries. Azerbaijan's GDP is approx. 6 times that of Armenia, meaning that their military budget is bigger than the entire government budget of Armenia.
So, on paper, Azerbaijan would be ready to launch a military offensive in Nagorno-Karabakh any day, if Armenian armed forces were the only obstacle to overcome. However, there is potentially a bigger obstacle: Russia. Obviously, Armenia's government want to secure Russian protecion, while Azerbaijan's government wants the Russian military to stay out of the conflict. So far, both have tried to curry favors with the Kremlin, but things are changing.
Why would Russia intervene on the side of Armenia? Because they want to keep Nagorno-Karabakh Armenian-occupied, for the same reasons why Transdnistria, Crimean naval bases, South Ossetia and Abkhazia exist: to keep these countries (Azerbaijan, Moldova, the Ukraine and Georgia, respectively) out of NATO. Here's how it works: because of Article 5, NATO never grants membership to countries with territorial disputes and non-NATO foreign armed forces on their soil; Russian military thinking measures Russia's security by the distance potential adversaries need to cover on their way to Moscow, as exchanging territory for time has been a time-honored (and mostly successful) strategy for beating back invaders. For numerous reasons (in which both parties share the blame) Russian military establishment considers NATO potential adversaries. Since the eastward expansion of NATO first into former Warsaw-pact countries and then into former Soviet republics, only very hard guarantees (preferably: Russian military bases) are considered reliable (and acceptable). These disputed territories and military bases are Russia's effective veto on the respective states' NATO membership. In case of Azerbaijan, Armenian forces substitute for Russians.
In case of Azerbaijan, keeping it out of NATO is especially important for the Russian government, as its NATO membership could very realistically (in their nightmare scenarios) change the strategic balance around the Caspian Sea and even threaten Russia with disintegration. Here's why. Right now, the Caspian Sea is the only sea with no U. S. naval presence. By contrast, Russia maintains by far the strongest naval force on that lake (and it is legally a lake, more on this later) and is essentially the arbiter of all disputes regarding seabed (oil & gas) and surface (fisheries, caviar) among littoral states. When separatists in Russia (in Chechnia or Dagestan) used the territory of neighboring countries (Georgia and Azerbaijan) for logistics and training, Russia's government did not hesitate to apply pressure with the threat of military force and in case of Georgia (in 2003) even acted on it carrying out a number of bombing raids in Pankisi Gorge against Chechen separatists, violating Georgian airspace and bombing undisputed Georgian territory, after deeming the efforts of Georgia's government (still headed by Eduard Shevarnadze at that time) insufficient. Azerbaijan has so far usually сomplied with Russian demands. When Georgia's new government (headed by Mikheil Saakashvili) declared its intention to join NATO and then moved to reconquer South Ossetia and Abkhazia (in 2008), the Kremlin responded with a full-scale invasion, the near-total destruction of Georgia's military infrastructure and the recognition of the two separatist states, maintaining a powerful military presence in both. Now, such measures won't work against NATO members. All parties know that.
Why are Russia's rulers so nervous about foreign support of separatism in the Northern Caucassus? Losing access to large parts of the mineral and caviar wealth of the Caspian Sea is just one reason. If Dagestan (which already has a simmering separatist civil war going on) and Kalmykia (a national republic with a 3/4 ethnic Kalmyk population) secede, it would become entirely feasible to close the small gap over the Volga delta between Kalmykia and Kazakhstan called Astrakhan county which right now on paper has a 2/3 Russian majority, but which may change very quickly. If Russia ceases to be a littoral state to the Caspian Sea, it loses its veto in re-classifying it from a lake to a sea. Once it is a sea, maritime law requires that access to international waters is granted to all without interference. This is why Turkey cannot stop any ships, including military ones, to travel between the Black Sea and the Mediterranean. In practice that would mean that American naval vessels could sail up and down the Volga waterway (which thus becomes an international one much like the Bosphorus) between St. Petersburg and Astrakhan and Russia's government cannot legally do anything about it. In Yaroslavl, they would be a mere 230km from Moscow and they are allowed to carry cruise missiles with nuclear warheads. As you can now understand, Russia's rulers would go to pretty extreme lengths to resist every single step down that road. Sounds crazy? See the first paragraph.
So how could Azerbaijan's rulers realistically hope to keep Russia neutral in an armed conflict with Armenia? For instance, by giving them a military base in Azerbaijan's territory. Namely, they rent them the Gabala Radar Station (a Soviet-era advanced beyond-horizon early warning station controlling the airspace over the entire Middle East). So, they could convincingly claim that they have a proper Russian military base and there's no need to keep those Armenian occupiers. The lease runs out on December 24, 2012. A few years ago, it was considered a given that it will be prologued after a little bit of haggling over the price and other minor horse-trading.
But things have suddenly changed last year. The rulers of Israel and the U. S. started preparations for an attack on Iran. For a number of reasons (more on this later), the Kremlin is against it and thus wants to make an attack on Iran as costly as possible. Ways to do that without getting involved in the conflict include providing Iran with effective air defense weapons and early warning in case of an attack. The latter even has the benefit of plausible deniability. The radar station in Gabala is perfectly suited for the purpose. In a surprise move, Azerbaijan's government raised the annual rent from $7.5M USD to $300M USD and offered to lease it for only seven years. This position has not changed for months and is still the official position of the government of Azerbaijan in the ongoing negotiations. Time is running out and Russia's military seems to be resigned to the fact that they will have to vacate Gabala before the end of the year; already half of the personnel has been removed, families have been resettled to Russia, etc. Whether or not the new radar station in Armavir is a suitable replacement is anybody's guess. This development points to the possibility that Azerbaijan got very strong security guarantees from the United States government, because it pushes the Kremlin unambiguously to the Armenian side in the Nagorno-Karabakh conflict. Given the value of Azerbaijan's support in the event of an attack on Iran, this does not strike me as entirely impossible. It is also worth noting that verbal guarantees and even strong military ties are obviously insufficient: the U. S. military stood idle as Russia's military invaded Georgia, even though they had direct access through the Black Sea; ferrying back Georgian troops from Iraq to Tbilisi was all the help Georgia got from Uncle Sam. Azerbaijan is not accessible by U. S. Navy, all material aid must arrive through Turkey or Georgia.
Armenia does not share a border with Russia and has no seaports either. Supplies from Russia (both for Russian troops stationed in Gyumri, Armenia and for Armenian recipients) must pass through third countries. Initially, it was done through Georgia, but since 2003 it has become increasingly difficult and by now effectively impossible. Azerbaijan and Turkey are out of question, which leaves the only possibility: Iran. Stuff gets shipped from Russian ports on the Caspian to Iranian ports; from there it is forwarded by land to Armenia. Thus, Armenia critically depends on Iran and its government is pretty desperate in keeping that relationship warm, even if it means breaching the embargo on pretty much anything and fouling up relationships with the U. S. and their allies. Here's the latest episode:
see also La Wik
For some, it may sound completely incredible that Armenia is on much better terms with Iran than with Georgia, but that's the relationship between governments, not the people. If it still sounds crazy, see the first paragraph.
Breaching the embargo on Iran is a huge business in which private and government organizations from all around the Caspian are deeply involved, albeit to varying extent. Remember, there is no U. S. naval presence. There are people in the U. S. embassies in all these countries whose main task is to collect all data that they can about oil shipments on the Caspian (which tanker arrived where, how much time did it spend loading or unloading cargo, etc.) and try to add up the numbers to figure out how many barrels of, say, Kazakhstani oil are actually relabeled Irani oil. Arrival and departure times of Russian container ships and tankers in the Caspian are strangely synchronized with the overflight times of American reconnaissance satellites (they always miss them). All Caspian ports are hiring personnel to deal with increased turnover. Iranian foreign trade is rapidly shifting from the Persian Gulf to the Caspian Sea. It has to.
At the same time, the relationship between the governments in Baku and Tehran have been deteriorating. Again, this has probably something to do with Azerbaijan's role in applying U. S. military pressure on Iran and security guarantees to Azerbaijan by U. S. government. I have very little information on the background but the fact remains that Azerbaijan's government is rapidly extending defense cooperation with the governments of Israel and the U.S. and severing cooperation with Iran's government and military.
Armenia's government is doing everything they can to raise the stakes to deter an invasion of Karabakh: it provides training, logistics and equipment to Kurdish separatists in Turkey, assists in breaching the embargo against Iran. As a side effect, they have essentially painted themselves into a corner. By now, Armenian diplomacy has lost all room for maneuver, they have firmly hitched their cause to anti-western alliances and — the large and somewhat influential Armenian diaspora notwithstanding — from a Western perspective, Armenia is ready for the Serbia-treatment, at the same time when Azerbaijan's diplomacy has more-or-less successfully maneuvered itself into being indispensable for the West for a number of strategic energy and military projects as well as the only friendly littoral state on the Caspian that is mostly free of Russian influence.
Thus, the thinly veiled threats about the imminent reconquest of Karabakh by Azeri officials should be taken seriously. They may well judge that Armenia's position is weak, the Russian Federation won't risk confrontation with the West. They have also signaled in no ambiguous terms, that they are absolutely not interested in reconciliation with Armenia until Karabakh is under Azerbaijani control.
If the American or Israeli strikes against Iran materialize, an Azeri invasion of Nagorno-Karabakh is very likely in my opinion; there is no way the Russian Federation will be able to provide any substantial military aid to Armenian forces short of directly attacking Azerbaijan from the north. Given how high the stakes are for the Kremlin, they might do just that in which case god help us all.
That is how I see it.