We can look for the cumulative trigger points of the Russo-Ukrainian war one by one from the levels of historical politics, NATO policy, geographical location, diplomatic relations, etc.
[1] Historical politics: On the surface, it is a contradiction between Russia and Ukraine, but in fact it is a contradiction between Russia and NATO. NATO is a military organization established by the United States and some European countries in the early days to oppose the Soviet Union, and later the Soviet Union collapsed, but the contradictions between NATO and Russia still exist. NATO has been sanctioning Russia for years, and NATO has been expanding eastward, from its initial 12 members to 30.
Crimea incident in 2014: Crimea is on the verge of the Black Sea, the Black Sea is russia's only sea passage through Europe, Crimea can not be lost, the land originally belonged to Russia but after the collapse of the Soviet Union to ukraine, but for various reasons Crimea referendum to join Russia, resulting in Ukraine's dissatisfaction.
[2] NATO policy: The two important conditions for joining NATO are, first of all, that there can be no state of war, and secondly, there can be no territorial disputes. Therefore, russia's war has led Ukraine to a state of war and does not meet the conditions for joining NATO.
[3] Location: Ukraine is located in the east of Europe, bordering Russia to the east, the Black Sea to the south, and Belarus to the north. Ukraine is geographically important and is the geopolitical intersection between the European Union and the CIS, particularly with Russia. Ukraine is extremely important to Russia economically and energy-wise militarily, not only as a military buffer, but also as a gateway to Europe.
Russia's western border is mainly Ukraine and Belarus. For Russia, these two countries are crucial. If Ukraine joins NATO, it is almost a siege of NATO countries for Belarus, which is extremely unfavorable to Belarus and may lead to Belarus joining NATO. This would lead to a serious threat to Russia's western border.
Blue for NATO countries
[4] Diplomatic relations: sanctions against Russia with the support of the United States and other representative countries for Ukraine.