Ukraine giving up it’s nukes was one of the reasons it was invaded. Also, the US promised to defend Ukraine incase it was attacked as part of the negotiations for them giving up their nukes, but that promise was broken.

For more info in the topic, see Ukraine and weapons of mass destruction

Ukraine inherited about 130 UR-100N intercontinental ballistic missiles (ICBM) with six warheads each, 46 RT-23 Molodets ICBMs with ten warheads apiece, as well as 33 heavy bombers, totaling approximately 1,700 nuclear warheads that remained on Ukrainian territory.[2] Thus Ukraine became the third largest nuclear power in the world (possessing 300 more nuclear warheads than Kazakhstan, 6.5 times less than the United States, and ten times less than Russia)[3] and held about one third of the former Soviet nuclear weapons, delivery system, and significant knowledge of its design and production.[4]

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In 1994, Ukraine agreed to transfer these weapons to Russia for dismantlement and became a party to the Treaty on the Non-Proliferation of Nuclear Weapons, in exchange for economic compensation and assurances from Russia, the United States and the United Kingdom to respect Ukrainian independence and sovereignty within its existing borders.[6][7] Almost twenty years later, Russia, one of the parties to the agreement, invaded Ukraine in 2014 and subsequently also from 2022 onwards.