A cite is proof that supports your argument. You should use them. I posted a statement explaining NATO's formation and purpose earlier. That was a cite.
The USSR's intentions were very clear after WWII. They wanted ro spread socialism and expand their territory.
This is a cite - one of many - that supports my statement.
https://www.shsu.edu/~his_ncp/Soviet2.html
The world did know precisely what their intentions were. I served with NATO in W. Germany for four years in the 1970s, and witnessed their aggression first hand. You may also wish to read about Poland and Czechoslovakia, postwar, and learn about their expansionist actions.
To say that the USSR did not declare their intentions is naive in the extreme.