France and Poland signed a treaty on Friday to increase cooperation on defence, nuclear energy and other measures, in a sign of growing alliances between European nations amid concerns about U.S. commitment to Europe's security.

Speaking ahead of the signing, Polish Prime Minister Donald Tusk called the deal “groundbreaking for our safety,” and made it clear this isn’t just about words on paper. The treaty includes a mutual assistance clause — meaning if either France or Poland is attacked, the other steps in.