Why did Russia attack Ukraine?

Russia attacked Ukraine on 24 February 2022. Ukraine suffered both civilian and military casualties. Immediately after the attack, the United States and other European states rushed to rescue Ukraine. Zelensky, the president of Ukraine sought support from the entire Western bloc. Western bloc helped Ukraine by sending advanced weapons. Russia has occupied more than 20 percent of Ukraine. On the other hand, Russia also sustained military casualties. The reason for attacking Ukraine may be more than one but the most important reason for attacking Ukraine is the historical rivalry between the United States and Russia. Since the Cold War, both the United States and Russia fought through proxies. Both states had military alliances. Russia the then USSR was having WARSAW PACT and the United States was having NATO. After decades of war, the USSR disintegrated in 1991. The WARSAW PACT disbanded after the disintegration of the USSR, however, NATO continued her expeditions. Recently, when NATO expanded towards Eastern Europe and the Ukrainian president tried to become part of NATO, President Putin of Russia opposed the decision by calling it a threat to the security of Russia. This caused the attack on Ukraine. Russia also has irredentist claims on the territory of Ukraine. The war is continuously increasing day by day and both sides are sustaining heavy losses.