1. The Confederacy gave an excuse to fire, but their reason was the preservation of slavery, as can be found in the "Cornerstone speech" of the Confederacy's VP.
2. You seem to be trying to say that the North was at fault for the entire war just because the North reacted to the attack on Fort Sumter with force. I mean, are you trying to say that when a nation is attacked, it should not respond in force?
3. And the fact that the North responded with force to the South's attack cannot in any logical way be likened to America fighting to "preserve the Shinto emperor".
4. In your last paragraph, you seem to be saying that the nationwide protests against police brutality is unwarranted and destructive to the nation. I would instead point out that what is unwarranted and destructive are the efforts of the racists and white supremacists to continue suppressing people of color.
You're an immigrant, and I'll always welcome immigrants - including undocumented immigrants. Immigration is what made our nation strong. However, it is unlikely that you are as aware of the sheer depth and breadth of racism in America, how it has affected our political and social landscape from our founding.
I know more about racism and what it has done to our nation than the great majority of my fellow Whites. You can read about some of my experiences here:
Here's something else that you might consider: when in all human history have you ever seen the majority ethnicity of a nation *peacefully* shift from one race to another? That's what's happening here. By 2045, the demographic trends are ensuring that America will be "majority-minority", and at some point beyond that, Whites will be a minority...but we'll still be America. As far as I know, this has never happened before in history - not peacefully.
That's why, while America is currently declining, we're not "committing suicide". We're changing. It's messy and loud and contentious, but this is what sets America apart from all other nations: only in America can someone come from any other nation and become American - not just in name, but in fact.
For instance, I can change my citizenship to Swiss or Russian or Australian or Chinese or Kenyan or Indian...but I can't become *truly* any of those in the eyes of the locals. Only in America (and to an extent, Canada too) can this be done. That's pretty special, if you'll think about it.
So...no, America's not "committing suicide". We're going though the same kind of national pissing contest that happened with the Rodney King riots in the late 1990's, and the Watts riots in the late 1960's. But we're getting better...
…and best of all is Trump's downward spiral into ignominy. At one point, his embrace of white supremacists would have been seen as normal. Today, it's seen by most of the public as shameful and repugnant. His time in the White House is the last great hurrah of the white supremacists. After this, they'll never have such a degree of power again in America.