Final answer:
In response to Russian expansionism, members of NATO, especially the United States, EU nations within NATO, and the United Kingdom, form the primary alliance against Russia, implementing sanctions and military support to countries like Ukraine.
Step-by-step explanation:
The question seems to refer to the geopolitical tensions following the dissolution of the Soviet Union and the alliances formed in response to Russian expansionism. The three out of the four nations forming an alliance against Russia would be the members of NATO, which includes numerous countries opposed to Russian hegemony. Particularly, the United States, the European Union members within NATO, and the United Kingdom have been at the forefront of opposing recent Russian actions such as the invasion of Ukraine. Historically, alliances like the Quadruple Alliance included different countries like Britain, Prussia, Russia, and Austria against common threats. However, in the current context related to Russian expansionism, the nations prominently acting against Russia include the United States, EU nations within NATO, and the UK, who have imposed economic sanctions and provided military support to affected countries like Ukraine.