Russia invaded Ukraine in 2022 under the pretense of rescuing Ukrainians from a fascist government and growing NATO influence. That excuse did not survive contact with the combative Ukrainians who were determined to repel the invaders and drive them from Ukraine. That is what is happening and Russia now claims they attacked Ukraine to annex it to Russia. This was considered necessary to restore Ukraine to its status as part of Russia. The Russian leader later claimed that he was seeking to restore other areas to Russian control.
Russia eventually named portions of Poland as one of its future targets for absorption into “Greater Russia”, otherwise known as the Russian empire. Belarus, the Baltic States and some former Soviet territories in Central Asia are also on the acquisition list. None of these targets for Russian aggression are willing to go peacefully. As the largest and wealthiest East European NATO member, Poland is leading the way by rearming to confront any future threat. After Russia invaded Ukraine, Poland decided to increase the size of the armed forces to 300,000 personnel and spend at least three percent of GDP on defense. NATO agreements suggest two percent of GDP but few European NATO members reached two percent. Now more NATO members are reaching or exceeding two percent and the increases are higher the closer the country is to Russia.
The NATO nations close to Russia or bordering Russia insist that if Russia is allowed to keep any Ukrainian territory, the Russians will attack them too as part of an effort to reconstitute the Greater Russia that the tsars and later communists created and maintained until 1991. Russian leader Vladimir Putin has always insisted that the dissolution of the Soviet Union in 1991 was a big mistake and must be rectified. Many Russians agree with that, but are less willing to pay the economic and military price that Ukraine demonstrated would result if Russia tried.
Kazakhstan, Azerbaijan, and Turkmenistan are nervous because they are, after Ukraine, according to Vladimir Putin, on the list of former Soviet territories that need to be reunited with Greater Russia. That would be difficult because these three states have growing economic ties with China and diplomatic ties with India.
Russia later expanded its territorial claims beyond Ukraine to include what it openly called Greater Russia. This is not quite rebuilding the tsarist or communist empires because Russia does not want the expensive to rule Central Asian states, but rather more lucrative territories Russian once ruled. This includes portions of Poland, all of the Baltic States and Finland, and parts of Alaska. There are some serious legal and practical problems with these claims. The United States has a larger military and nukes which might come into play to deal with efforts to enforce any Russian claims on Alaska. Russia is making claims on several Eastern European NATO members who are protected by the mutual defense clause of the NATO treaty.
Russia and all the nations involved are members of the United Nations. Article 51 of the UN charter demands that members refrain from the use of force against the territorial integrity or political independence of any state. Russia says this does not apply because Ukraine is a breakaway part of Russia and Russian troops are seeking to liberate Ukraine from foreign (NATO) oppression. Ukraine is also a UN member and protests Russian claims as well as the UN tolerating the Russian use of its Security Council veto to block any serious UN opposition to the Russian aggression.
Ukraine pointed out that the Ukrainian forces will force Russian troops out of Ukraine and then the problem will be what the rest of the world does with Russia.