Because the EU in itself is a pact of no agression between european countries?
Before that it was a fuckfest, name a country in Europe who hasn't been invaded at some point in time by a neighbouring state
Before that it was a fuckfest, name a country in Europe who hasn't been invaded at some point in time by a neighbouring state
NATO is only defence in military sense from external threats.
Internal relationships are much broader: trade, laws, internal politics, multi-country alignment towards same goals, even goal definition etc. there is european parliament where representatives from all member countries gather and discuss a lot of different topics. none of that provides NATO.