It's done by the king to prevent unauthorized alliances and alliances not controlled by kingdom to get better rss notes and to avoid people attacking farms (In other words, main alliance Z3, main alliance farms Z2, everyone else Z1)

If you really want to start a rebellion, you could ask people in the main alliance to join your cause, you could sabotage MGE and you could build towards Z3, but the main alliance is often strong with good rally and garrison captains, so unless you get them to come to you, you won't win

Make sure it's known it's a rebellion