The earlier campaigns were not designed with the eventual gameplay changes made in latter versions in mind, so you'll need to fire up DL/DA to play those campaigns.

That's strange. I have GalCiv2 Ultimate, on DVD, and I could launch the three campaigns from the in-game main menu.

I started with the Dread Lords campaign. The first three missions seemed to be 'research planetary invasion, then invade one planet'. The fourth (might be counting wrong) seems to be 'research planetary invasion, but get invaded by vastly superior forces before you can invade the one planet that's your objective'. At that point I gave up.