There was an agreement between Russia, Ukraine, the United States and UK that guaranteed the territorial integrity of Ukraine. In return, Ukraine gave up over 1,000 nuclear weapons it had inherited from the USSR. The Budapest Memorandum on Security Assurances from 1994 was exactly the "easy" fix "multilateral security agreements" can accomplish, according to you. How did that work out? You demonstrate a lack of basic knowledge. I suggest you avoid speaking on topics you know nothing about.