I've been thinking about a strategy that might help against militant tyrants like Putin. If he attacks, just let the soldiers enter without resistance. When the army starts to control civilians, record everything possible (who is doing what) and share that on the internet. Let the army know that people are obeying them only because they threat with violence. If they don't threat, then nobody should obey them. When they do threat, record it and publish it.
When there is enough evidence of foreign army taking control, an anonymous online "defence force" should start to publish kill orders for high ranking intruders. Basically ordinary citizens could create a considerable threat of assasination against all new leaders.