https://www.rferl.org/a/lithuania-soviet-crackdown-1991-krem...
https://www.rferl.org/a/lithuania-soviet-crackdown-1991-krem...
You seem to comment to better inform readers, yet your comment distorts the truth.
Even the article you linked talks about Lithuania declaring independence from the USSR, not asking for democratic reforms.
Despite what your article says, if you read the story on Wikipedia, Lithuania did in fact unilaterally declare independence from the USSR in March 1990.
Just as an example, check what Spain did in 2017 when Catalonia tried to declare independence after a popular vote. If Catalonians decided to resist, there is no doubt that the Spanish state would have used violence to suppress them. Try to imagine what the USA would do if any of its states tried to declare independence.
It's an intriguing historical question what would have happened if Fort Sumter hadn't been attacked. Would the Union have eventually made the first move? Would peaceful negotiations have eventually resulted in some stronger guarantee in the continuance of slavery and an end to secession? Would the Union have eventually dissolved amicably?
Going by what happened during the Nullification Crisis, the answer is likely a "Yes".
You might be able to have a little fun with the first option -- the Union attacks first -- but it's still going to largely end up political questions:
1. If the Union attacked immediately after South Carolina seceded, how would it have changed which States would follow suit?
2. If the Union attacked in 1862, would more States have seceded by then?
3. Would the Union have lost any supporters -- either notable generals or even member States -- if it had fired first?
After those political questions are answered you could have fun wargaming out the subsequent war with new sides, but trying to answer the political questions is not as easy or fun.