The reason to bring up NATO is because it's the military alliance of the world's imperial core. Imperialism, as Marxists understand it, is an economic process by which the oppressed nations are fleeced of the bulk of their surplus value. Europe, the US, and the rest of the imperialist powers perform this process through domination of monopoly finance capital, and enforce it through the hundreds of NATO military bases around the world (typically US, but also European).