Just Cause Theory
“a three-step theology of resistance…
“The  first was prophetic denunciation of the civic evil. When the magistrate is defying God, then courageous men in the pulpit should be authoritatively naming what is happening, and denouncing it ( Matt. 14:4). The  second stage is for the believers to flee the persecution. Jesus said to do this — when you are persecuted in one city, flee to the next (Matt. 10:23). The  third and final stage is to take up arms defensively (1 Sam. 22:2). David’s men were armed, and were not cooperating with Saul’s tyranny at all, and would certainly have defended themselves if cornered, but David would still not lay a hand on the Lord’s anointed. So it is not permissible to undertake a revolution whereby the rebels seek to overthrow the existing authority. But taking up arms defensively is an option. And stating that you will refuse to comply if required by the tyrants to is also an option. This is why George Washington said that weapons were liberty’s teeth. This is why molon labe is an option. As the saying goes, when the government starts saying that you don’t need a gun, then you need a gun.
“In his magisterial Institutes, John Calvin gave us another layer of protection against lawless anarchy. He taught that when the supreme ruler is resisted, it should be undertaken by the lesser magistrate, and that the people should not try to resist tyranny at the top as an inchoate mob. They should resist tyranny from the central government by means of submission to local authorities who are fulfilling their oath of office. Every lesser magistrate has the obligation (not the right, the obligation) to disobey unlawful orders from above. And, when they do this, the people have an obligation to rally behind them.
Just War Theory
“[W]e can evaluate whether… any decision leading to hostile action, is justified according to what is called “Just War Theory.” Over the centuries, Christian thinkers from Augustine to Aquinas to the Reformers—seeking to reconcile Christian teaching on the sanctity of human life with the Christian responsibility to love our neighbors by protecting them from evil—have proposed a set of conditions by which a violent act can be considered justified. These conditions deal with both whether war ought to be waged, as well as how war should be waged.
“ First, the cause for going to war and the intention behind it must be just.  Second, the war must be waged by a legitimate authority.  Third, force must be used as a last resort.  Fourth, force used in war must be proportionate to the threat.  Fifth, force must not target non-combatants, and finally,  there must be a reasonable chance of success.”