What about top US political scientists such as Mearsheimer? Your tribalistic approach to this issue betrays the inability to reflect critically.

Putin did not invade Crimea. Crimea declared independence after the US instigated a coup against the elected gov't in 2014. Crimeans voted in a referendum to join Russia. Most Crimeans are Russian. It was part of Russia rather than Ukriane for most of its history. Khruschev was the one who gave it to Ukriane in the 50's when both Russia and Ukrane were in the USSR.

@Krish55 it wasn't Russian until the late 1700s so perhaps the Turks and Mongols should control it.

The referendum was conducted by Russia. Russian soldiers were already in control of Crimea when the referendum happened and the results are not recognized by most Nations.

"2014 Crimean status referendum - Wikipedia" [en.m.wikipedia.org]

"Demographics of Crimea - Wikipedia" [en.m.wikipedia.org].

@Lorajay
Turks and Mongols are not an issue over control of Crimea now. Just as Mexico isn't an issue over the control of Texas and the Southwest now. But if you want to make the former relevant, then perhaps the latter should also be relevant...

Once again, remember that Ukraine would not have lost Crimea had the US not overthrown its government in 2014. Russia could not allow a NATO port in Crimea.

German Mag. NATO broke its promise: [spiegel.de]

@Krish55 Nothing was ever signed, much less ratified. Russia is an aggressor nation in this case and to defend their actions is to defend the murder of innocent women and children and be complicit in their war crimes. Russia invaded a sovereign nation.
from the article: But that’s not all. At the end of January, Russian Foreign Minister Sergei Lavrov wrote an open letter to his Western counterparts in which he cited additional understandings. In particular, he focused on the Charter for European Security, rooted in agreements reached in 1990. East and West had concurred at the time that every country has a right to freely choose the alliance it wished to be part of, while also emphasizing the "indivisibility of security." ...
In doing so, the West didn’t break any treaties, but some participants were concerned nevertheless. Years later, Genscher said that the expansion was just fine from a formally legal point of view. But it was impossible to deny, he said, that it was counter to the spirit of the understandings reached in 1990.

@glennlab and counter to common political sense.