The naval conflict this weekend between Russia and Ukraine was not a sudden development. Pressure has been building between the two nations for a long time, arguably even before Ukraine broke away from the disintegrating Soviet Union in 1991.

Following are the key factors in a dispute that is coming dangerously close to a major military confrontation.

The Orthodox Schism: Humming beneath the surface of the Russia-Ukraine conflict is a schism in the Orthodox faith. Western observers often underappreciate the importance of religion to Russian President Vladimir Putin’s political success. Top Putin officials who are not even Christian make a point of getting themselves photographed in iconic locations to reinforce the link between the Orthodox church and Russian government. Putin’s personal mythology includes his childhood as a secret Christian during the Cold War dominance of atheist Communism.

Ukrainians have long complained about Putin using the Orthodox church as a vehicle for spreading his influence through the former Soviet republics. Ukrainian believers scored a big win in October when the archbishop of Constantinople defied the Kremlin and granted permission for Ukraine to establish an independent church for the first time in almost 250 years.

Ukrainian President Petro Poroshenko hailed the decision as a blow to the “imperial illusions and chauvinistic fantasies of Moscow” and explicitly linked the establishment of the church to Ukraine’s quest for secure nationhood.

Russian Orthodox leaders denounced Archbishop Bartholomew, questioned his legitimacy, and stated their refusal to recognize the independent Ukrainian church. They also suggested Bartholomew was acting as America’s agent on a mission to undermine Russian authority. The Russian Orthodox church soon declared itself out of communion with Constantinople, whose headquarters is nowadays referred to as “Istanbul” by most of its residents – although Putin conspicuously used the older name during a happier moment in his relationship with Archbishop Bartholomew this year, to the consternation of the Turkish government.

The bottom line is that the Orthodox schism is among the most significant events in the 1500-year history of the faith, and both Kiev and Moscow clearly appreciate its political ramifications. The prospect of losing religious influence in Ukraine may have led Russia to take a more aggressive position against Ukraine. It is also useful for Kremlin-friendly media in Russia to stoke fears about Ukrainian “radicals” attacking or seizing churches owned by the Moscow patriarchate.

The Sea of Azov: The Sea of Azov is enormously important to Ukraine and to any Russian plan for seizing the crucial Ukrainian seaports of Mariupol and Berdyansk. The Russians have slowly amassed the naval power they would need for such an operation, while Ukraine struggles to counter with its own military buildup.

Russia and Ukraine signed a treaty in 2003 that sought to make the Sea of Azov freely accessible for commercial traffic from both nations while keeping military activity in check. In this weekend’s naval clash, Russia claimed the Ukrainian ships did not properly notify Russian authorities of their intended movement as required by the treaty.

Russia strongly objected in October to Ukrainian plans for purchasing surplus U.S. Navy vessels and training with NATO forces in the Sea of Azov, claiming such actions would violate the 2003 treaty. Ukraine’s President Poroshenko responded to these complaints by declaring, “We are getting ready to repel Russian aggression from the sea in the Sea of Azov area. Powder should be kept ready.”

Russia warned in September that if Kiev takes steps to abrogate the Sea of Azov treaty, it will “trigger certain consequences for both Ukraine and Russia.” Ukraine has complained about Russian violations of the treaty for years and occasionally entertained legislation that would terminate the treaty. One theory for Russia’s actions over the weekend is that Moscow wants to provoke Kiev into declaring the treaty dead so Russia can take even more provocative measures.

The Kerch Strait and Crimea: The Sea of Azov connects to the Black Sea through a narrow passage called the Kerch Strait, which also happens to be the body of water separating Crimea from Russia. After the Russians annexed Crimea in 2014, they swiftly set about building a bridge across the Kerch Strait. This is the bridge that appears in many photographs of the Russia-Ukraine naval confrontation on Sunday.

The 12-mile-long bridge was formally opened in May by President Putin, who ostentatiously drove across the span in an orange truck and declared the bridge a “miracle” dreamed of by Russians since the time of the tsars.

The United States and European Union slapped sanctions on Russian individuals and corporations involved in building the bridge, which was denounced as a “violation of international law” and threat to Ukraine’s “peace, security, and sovereignty” by the U.S. Treasury Department.

The Kerch Strait bridge is certainly convenient for auto traffic, which previously had to rely on slow ferries at the mercy of the weather. Unfortunately, it is very inconvenient for large ships attempting to pass through the strait, because the span was not made high enough to accommodate them. According to Ukraine, this was a feature of the design, not a bug.

Trade to Ukraine’s ports on the Sea of Azov is down by up to 30 percent, due to both the bridge construction and Russia’s habit of hassling Ukrainian vessels attempting to pass through the strait. Russia claims enhanced security is necessary because Ukrainian extremists have targeted the bridge for destruction. Thousands of Ukrainian jobs depend on heavy industry that relies on shipping in the Sea of Azov, especially the port of Mariupol, which has already been seized and briefly held by pro-Russian separatists once before.

If Russia wishes to weaken the Ukrainian economy and create political turmoil that strengthens pro-Moscow parties, in a strategy similar to the one China pursues against Taiwan, Putin could scarcely do better than restricting traffic through the Kerch Strait. This would also help Russia isolate and quickly destroy Ukrainian naval forces in the Sea of Azov.

Ukrainian politics: Elections in Ukraine are scheduled for March. The Russians are accusing President Poroshenko of provoking a crisis in the Sea of Azov so he can declare martial law and suspend the election, which he is currently expected to lose. (The favorite to win is Yulia Tymoshenko – who is, if anything, even more pro-European Union, pro-NATO, and anti-Russia than Poroshenko, but also has a legal history Moscow might be able to exploit to weaken her after the election).

Poroshenko did indeed issue a decree imposing martial law on Monday, effective for 30 days beginning Wednesday, but he stipulated the decree would not interfere with the elections in any way. Three former Ukrainian presidents nevertheless wrote an open letter on Monday objecting to Poroshenko’s degree and warning that martial law poses a “threat to democracy.”

“The martial law declaration adds further instability to the situation, especially since the Ukrainian parliament will most likely approve it, if with some reservations about its potential effect on domestic politics. Russia could use it to justify stronger military action, arguing that Kiev is moving to a war status,” Alx Brideau of the Eurasia Group warned on Sunday.

Sanctions against Russia: The Western world is lining up behind Ukraine, with allies like Poland and Estonia immediately calling for sanctions against Moscow. Russian stocks and currency slid on Monday morning as the possibility of new sanctions loomed.

Some analysts speculated Putin wants to provoke more sanctions so he can blame Russia’s economic woes on foreign interference. Others noted Russia has a habit of provoking crises and ratcheting up tension in advance of major international meetings such as this week’s G-20 summit in Argentina.

Putin might also want to demonstrate his defiance of international sanctions. Russia works to undermine sanctions against countries like Iran and North Korea and often challenges the entire concept of sanctions as an immoral instrument of Western imperialism.

“It’s obvious that this painstakingly thought-through and planned provocation was aimed at igniting another source of tension in the region in order to create a pretext to ramp up sanctions against Russia,” the Russian Foreign Ministry sneered in a statement on Monday.

“We’d like to warn the Ukrainian side that the policy of provoking a conflict with Russia in the area of the Sea of Azov and the Black Sea, which has been pursued by Kiev in coordination with the United States and the European Union, is fraught with serious consequences,” the Foreign Ministry added.