Men armed with knives killed a British soldier in London, then said it was revenge for killing Muslims.

The jihadis' theocratic agenda is horrible tyranny, but they have a valid grievance about US-UK violence. On this occasion they attacked a military target, so if you want to think of this as war, the attack was not a war crime. However, they threatened to attack civilians, which would be a war crime.

The US admitted that four US citizens were killed by US drone attacks.

The US and UK should stop killing civilians around the world. Whether they are Muslim (as is usually the case today) or Christian (as was typically the case in the 70s and 80s) is an insignificant detail.