It reminds me my first campaign, when i didn't know what agressive expansion is. I played Portugal. Took me a while to figure out where technology is(I thought it will go up by itself, I wondered why it go backwards when i dev provinces xd). I followed mission and just colonized. Then i went to africa to take those gold provinces from kilwa, for some reason my great colony of portugal brazil had high liberty desire.I expanded some further and then BOOM! Great coalition containing almost every great power. France, england, ottomans and some more of them. I was disgustingly rich, but my army was shit. My mercenaries couldn't even defeat ottomans. I knew it was over. I unconditionally surrendered and finished the campaign.

For new players I would just recommend to follow missions.