Any one of five countries can block a UN Security Council resolution

When the UN was founded in 1945, the wartime victors, the US, Soviet Union (now Russia), UK, France and China, became permanent Security Council members with the power to veto any substantive resolution. The Soviet Union dominated its early use, and the USSR and Russia have used it most often, followed by the US. Critics say the veto paralyses the council; defenders say it keeps great powers inside the UN.

— Wikipedia contributors, United Nations Security Council veto power — UN Charter, Article 27