"Modern" Clical Music?

Why does it "seem" that this century's, and most of the last century's clical music composers created music which at the very least is discordant and very aggressive. I used to suppose it was because of the turbulent times but wow, if you consider Beethoven's most famous symphonies were written to give to Napoleon for this or that war. Or that certainly other composers of the time worked for this or that king or prince either having gone to war or just going, that theory doesn't hold water. The other theory I was entertaining was that the "famous" works, or those done by "masters" of centuries long gone were just so "done"! But now I realize that I just don't have a clue. A little help please! Thanks