"Just as ruthless and indifferent to the rule of law as his predecessor." Ouch.

[loose wheel]

184. Countries are also not allowed to harbor combatants

If some persons or organization within a country attacks across international boarders, the country they attacked from or are living in has a requirement, under international law to surrender those persons or those associated with that organization to the attacked country. Ordinarily, the country that attacked would approach the harboring countries and demand the surrender of those persons, and even demand compensation from the country of citizenship.

In practice, people who do the sort of thing that terrorists do aren't hiding in a country that is particularly friendly to their target. If the country they are in will not or can not capture and extradict the attackers, then that country can, under international law, be invaded. It has happened before.

After Pancho Villa raided Mexico, President Wilson determined that Mexico would not be able to capture and extradict Pancho Villa so he launched the expedition into Mexico.

Britain hung a Captain of a warship that attacked a French ship after the treaty of Paris ending the Seven Year's War because it was either that or renewed conflict.

Uruguay required that the Graf Spree leave port in twenty-four hours, the max international law would allow, because any longer than that, the British could have attacked the port, and it would have been perfectly legal.

Hitler used a false flag operation against Poland to claim that cross boarder attacks had occured to justify his invasion.

International law only requires that efforts to prevent civilian casualties be made, not that no civilian can be killed. A hospital, for example, is not a legal target. However if a sniper is using a room in the hospital then the whole building can be destroyed and that would be legal. A religous building is not a legal target, but if intelligence determines that it is being used to store weapons it becomes a legal target. The Geneva convention is no more a suicide pact than the US constitution.