What causes the Treaty of Brussels from happening?

[HappySack]

So I was playing democratic Germany and enforcing peace on others, especially the U.S.S.R and long story short we freed France and the U.K. from communism and turned the U.S.S.R into a Jackson Pollock painting and later we all removed Fascism from Italy.

But the Treaty of Brussels happened and everyone left my faction except France, and a very few handful returned since then.

Is is because Russia and France both existed independently or did I need to puppet or annex them to stop this from happening?

[Guest In Disguise]

it is only Russia/U.S.S.R that dicate the treaty of brussels for happening because it is forming of NATO which was a alliance to combat Soviet Union.
So if russia is annexed there would be no reason to form treaty of brussels because there is no russia/Soviet Union

Edit: if Russia/Soviet Union is part of the Allies it will also not trigger the treaty of brussels

[HappySack]

Thanks, so annexing them is the only thing I could have done.

Puppeting or even having them join my faction wouldn't be enough then.