Russian–Ukrainian Friendship Treaty

The Treaty on Friendship, Cooperation, and Partnership between Ukraine and the Russian Federation, also known as the "Big Treaty", was an agreement signed in 1997 between Ukraine and Russia, which fixed the principle of strategic partnership, the recognition of the inviolability of existing borders, and respect for territorial integrity and mutual commitment not to use its territory to harm the security of each other. The treaty prevents Ukraine and Russia from invading one another's country respectively, and declaring war.

Source: Wikipedia — Russian–Ukrainian Friendship Treaty (CC BY-SA 4.0)