Everything you need to know about NATO as it turns 70 this week

Since its Cold War inception, the North Atlantic Treaty Organization has been keeping Russian aggression in check as an increasingly fragmented Europe has shifted and moved over 70 years. Founded in 1949, the alliance started off with 12 members but has grown over the years to 29 member states. Even as the Soviet Union gave way to the Russian Federation, the alliance has cemented its status as the bulwark that keeps Western Europe free.

A lot has happened over 70 years. Political shifts in member countries caused members to rethink their role in the alliance. Russian threats kept many members out for a long time – and still does. And the mutual defense clause, Article V, was invoked for the first time ever.

There were 12 founding members.

Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States founded NATO on April 4, 1949, as a hedge against growing Soviet power in the east. The centerpiece of the alliance is Article V, which obliges member states to consider an attack on a NATO ally as an attack on itself and respond with armed forces if necessary.

The alliance is more than a bunch of disparate parts, it has a unified military command that guides its strategy, tactics, and training on land, on the oceans, and in the air, complete with its own installations and command structure.

You might know of the first Supreme Allied Commander.

An American is always at the top.

The alliance is organized almost like the United States' command structure. A Chairman of the NATO military committee advises the Secretary General on policy and strategy. The second highest position is the Supreme Allied Commander, always an American general, who heads the operations of the alliance in Europe.

The United States, Britain, and France are currently the most powerful members of NATO, but after the U.S., only Greece, the United Kingdom, Estonia, Poland, and Romania met NATO spending standards. Greece and Estonia are the second-highest spenders as a percentage of GDP.

"Paix en quittant."

Countries actually left NATO.

Many balked at the idea of the United States leaving the alliance, as then-candidate Trump threatened to do while running for President of the United States. While the U.S. withdrawing from NATO would be a disaster for everyone, a member country leaving NATO isn't unprecedented.

France left NATO between 1966 and 2009 because President Charles DeGaulle resented the idea that France wasn't on an equal military and nuclear footing with the United States and wanted more independence for French troops. Greece left between 1974 and 1980 because of a conflict with NATO ally Turkey.

This is as close as they get. Right after this photo, they raided English coastal towns. Because tradition.

One member doesn't have an Army.

Iceland doesn't have a standing army (it has a Coast Guard though!) but is a member ally to NATO anyway. The island nation actually does maintain a peacekeeping force of troops who are trained in Denmark, but Iceland joined the alliance on the condition that it wouldn't have to establish a standing army – NATO wanted Iceland because of its strategic position in the Atlantic Ocean. The island is protected by the Canadian Air Force.

Poland will no longer be taking Russia's sh*t. Ever again.

Former enemies have joined NATO.

With the fall of the Soviet Union came a slew of countries who were much smaller than their former Soviet benefactor. Many of these countries were once members of the Warsaw Pact, the USSR's answer to the West's NATO. In order to keep former Soviet Russia from meddling in their newly-independent domestic affairs, many Warsaw Pact countries who trained to fight NATO then joined it, including Albania, Bulgaria, Estonia, Croatia, Hungary, Latvia, Lithuania, Montenegro, Poland, Romania, Slovakia, Slovenia, and (after the unification of Germany) East Germany.

Pictured: Why Georgia wants to join NATO.

New NATO members could trigger the war it was designed to prevent.

The alliance is always courting new members to counter the threat posed by Russia. This means eventually NATO had to start looking east to find new partners – and many were willing. Unfortunately, pushing eastward puts NATO troops on Russia's doorstep and there are certain countries that Russia considers a national security threat were they to go to NATO. Two of those, Ukraine and Georgia, have seen Russian invasions of their territory in the past few years in an attempt to thwart their eventual membership.

Russia warned NATO of a "great conflict" should either of them join the alliance.