You use flags, right? You can increase the money on a flag to entice your troops to go there.

Works perfectly fine for me.

Yeah. I was setting flags on enemies, building, islands and I would still have people sitting around the campfire rather than doing anything.

After struggling through a couple of missions, the objectives/tutorials finally introduced me to camps which lead to raids. Camps are a building you don't build but tell your units to build using the radial menu (like attacking). You can then tell the camp to raid an island, then they move as a group (4, 6, or 8 depending on camp level).

The management of what units are selected for the camp could use improvement, but that is a UI thing that could probably be improved in a patch.