(NewsNation) — News that Sweden and Finland were moving toward NATO membership infuriated Russian President Vladimir Putin, but Finnish President Sauli Niinistö told Putin, “You caused this. Look in the mirror.”

After deciding to apply to join NATO, a country has to put in a formal application, this will then go under consideration by NATO to make sure the country meets standards for membership.

The most elemental necessity for membership in NATO is location. NATO stands for North Atlantic Treaty Organization, so a country in, say, South America wouldn’t be eligible for membership. It’s interesting to note that 18 countries have joined NATO since the original 12 (Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States) founded it in 1949. None have left.

In keeping with its original purpose of staving off the threat of the USSR, NATO is limited to countries that are democracies. Similarly, members must have market economies run by the principles of free enterprise, not the state-driven system used by the Soviets and other totalitarian regimes.

Finally, given that NATO is a military organization at its base, a prospective member country needs to prove that its military can not only protect the prospective member but add to the security of the organization as a whole. During the Cold War, the U.S. footed the bill for a lot of the military hardware and personnel deployed in Europe, but that balance is shifting now that more NATO countries are beefing up defense.

The vote to approve membership in NATO must be unanimous, and then the new country’s own governing body has to vote to approve the membership.

It’s expected that both Finland and Sweden will be starting the process soon, and there don’t seem to be any huge roadblocks to both being approved in short order.