Let's look at Ukraine.
There it is, in the center of this map.
North of the Black Sea, west of Russia, east of Central European countries of Poland, Slovakia, Hungary, and Romania.
Ukraine is part of the greater Russian/Slavic world. Ukraine was sometimes part of Russia, sometimes part of Poland, sometimes part of the Polish-Lithuanian empire, briefly part of German occupied territory, during WWII. For most of the past century it was part of the Russian empire. Currently, it is independent.
Depending on whether or not one includes Crimea and the now-contested regions in the east, Ukraine has 40 or 44 million people. Russia has about 140 million. Ukraine is either a big part of Russia, or a big re-acquisition for it. Here is how Stalin would have seen the population distribution. Ukraine is the densely populated dark area in the southwest.
The pattern persisted:
Moscow, with ten million people, is visible northeast of Ukraine. (Remember, Ukraine sits atop the Black Sea.) Kiev with 2.6 million people is visible in north central Ukraine. Ukraine's second city, Kharkiv, with 1.5 million people is visible near the Russian border, north of the Black Sea.
Ukraine, Belarus, and the three Baltic states were fully part of the USSR. Another tier of countries, including Poland and East Germany, south to Bulgaria, were part of the "Russian Block" of quasi independent Russian-controlled countries.
That penetration west is not new. Here is Russia in 1914:
Russia has two fundamental strategic problems. The first that it is landlocked during a time of war. Its exits to the world's oceans are easily blocked by foreign rivals. Turkey, and before that the Ottoman Empire, has been a traditional southern rival of Russia, contesting control and influence in the Balkans and Russia's Black Sea and Caspian Sea regions. Turkey's great threat is Russia, which would like to control the Bosphorus. Turkey aligned with NATO, the worst of outcomes for Russia. Russia's second problem is its vulnerability to attacks from land armies coming from the west across the broad northern European plain. NATO expansion to Poland and the Baltic States put NATO troops within 100 miles of Russia's second city, St. Petersburg. Russia lost the strategic depth that protected them against Napoleon and Hitler.
There is an ongoing imperative for Russia to address those two strategic vulnerabilities. That imperative conflicts with a contrary one. European powers over the centuries work to suppress any European power from becoming too strong. Sometimes that power has been France, with Britain and Europe united against it. After Germany unified under Prussian leadership, France and Britain aligned with Russia/USSR to confound Germany. More recently they align with Germany to confound Russia/USSR. Poland, Belarus, and Ukraine were and remain the victims to be saved, abandoned to their fate, or devoured.
Russia has a large military, nuclear weapons, and the tool of its oil. It wants to change the equilibrium. Another tool for Russia is the fact that the borders and ethnicities of the battleground areas have never been settled, and they sometimes conflict with an ethic of self-determination. The Washington Post reported that four of six people in Ukraine speak Ukrainian; one in six is both ethnically Russian and speaks Russian. Another one in six is ethnically Ukrainian and speaks Russian.
The fight over Ukraine is another iteration of European great power politics. Russia wants something. The West doesn't want Russia to have it. The West wants the strategic depth for itself.
So we fight on, endlessly.
Tomorrow: More maps. Ukraine is a breadbasket and food exporter.
Back in the 1980s after spending a lot of time doing research as visiting scholar to universities in Poland and Czechslovakia (as well as a lot of mountain climbing and bird watching with colleagues, I read several history books. These unique ethnicities would periodically be clobbered from the east (russia), the west (Prussia) and the south (Austria-Hungary). Tough people to have survived with customs and languages intact. Late 1800s Polish linguists had to recreate Polish, a slavic language which doesn't look anything like Slovakian, Ukrainian or Russian.