Why must Putin invade Ukraine in order to prevent that nation's integration into Nato or the EU?

If he owns it, by occupation, NATO can’t take it away from him. He could wreck the place, but then it isn’t any good for anyone, so why bother??
Putin wants the old USSR back, and this is his way of pushing for that end.
Who’s next??

That’s not Putin’s goal. He doesn’t really gave a crap about Ukraine. Maybe a little, but not like you would think.

He’s a weak leader, his party is known for its corruption, he’s a dictator. He gas put down any opposition in his party, so all decisions go to him.

The Russian economy is in bad shape, industry is failing, and his population is finally getting tired of his embezzlement and billions and his leader-for-life shenanigans.

So what do you do, if you’re a leader of a country that is failing? You make up a war, of course, to rally the population with nationalist fervor so that you can hold your power. You point your finer at the outside enemy.

THis is a tried and true methoid:

- Ayatollahs in Iran blame ‘the Great Satan’ (the USA) for all of their problems, so the Iran doesn’t need to treat its people right.

- US did it in Afghanistan and Iraq after 9/11 (Baby Bush wanted to appear tough!)

- JFK and LBJ chose to fight the Viet Nam war becuase of the evil commies

- Clinton bombing a factory in Libya just as the Lewinsky scandal broke. And then bombing Iraq during the Clinton impeachment trial.

- to some degree, Hitler struck back at Europe because he wanted to blame Europe for the economic conditions in Germany after WW-I.

and there are probably dozens of other examples if I really wanted to spend the time.

Watch the movie Wag the Dog about a made-up war to get peoples’ minds off a presidential sex scandal.

Summary: This isn’t about Ukraine. It is about Putin trying to save his own ass.

Save his ass from whom? He’s the most popular leader Russia’s seen since Lenin himself. His people just adore the way he stands up to the West, and all of those Russian descendants Stalin transplanted to Ukraine are just begging him to “liberate” the place and “reunite” it with “Mother” Russia.