But trials and kidnapping are a lot of work why not save time and just shoot him?
That "attitude" (the more murderly-minded attitude, not the lighter attitude that I presume you're taking), is why countries like the USA can't recognize the ICC.
The idea of a "assassination" always births the idea of "just retribution" and it always escalates to "just war", and there is no "just war" that doesn't involve killing lots of civilians somewhere, which is where "war crimes" come from. Desert Storm was a good example of a "just war" that was carried out successfully, but what happened both before and after in that region? Back 1910-ish, the UK set up British Petroleum to secure future oil supplies by supporting state overthrow in the Gulf region (were assassinations involved? well, delivering military equipment is "a lot of work why not save time and just shoot him"?).
The core problem is that when some people from First Country take actions against people in Second Country, actions that would be illegal if taken in their own country, and First Country does not treat them as law-breakers, First Country has given Second Country a just cause for retribution.
Examples...
- France "conquered" Vietnam and 90 years later the US was dragged into a "just war" in Vietnam.
- UK "conquered" Iraqi/Iran and 90 years later the US was dragged into a "just war" in the Gulf region.
I expect there are other examples of how the "just assassination" can lead to "retribution" and "just war" and "war crimes", because there is plenty of South America and Africa "colonization" history I know nothing about, but over and over, it goes back to failure to hold accountable those who break your country's laws in other countries.
It is no different than if a kid in your neighborhood is escalating their bullying actions against other kids to physical violence and theft. Do you, as an adult in the neighborhood, find the kid and break a few bones? Or, do you gather the other adults and determine a group action, to attempt to force the parent to shut their kid down, or even to escalate to take the kid out of the parent's control and into "custody"?
If your "tribe" doesn't follow the rules of your tribe when dealing with other tribes, they need to be persecuted and prosecuted by your laws. Failure to do so will always lead to future conflict.
This conflict with Russia invading Ukraine, this is just "colonization version n.nnn". It was done to maintain Russia's economic control of cheaply produced and cheaply transported natural gas into the EU, to prevent Western businesses from using Ukrainian reserves to replace Russian piped gas into the EU.
This is
extremely flawed. To begin with, drawing a straight line from British colonialism in the 1910s to the Iraqi invasion of Saudi Arabia is pretty sketchy. The British
did put in the government that was overthrown by the government that was overthrown by the B'aathist movement that eventually put Saddam in power, as part of the dissolution of the Ottoman empire following the First World War. It is also accurate to say that the Pan-Arab movement that overthrew the Hashemite monarchy was motivated by a Arab nationalist movement that wanted Foreigners Out, but the inciting incident was more complex than mere colonialism - the Hashemite king had entered into an alliance with other states in the region (under British advice) that led to severe tensions with Egypt. Egypt eventually responded to these tensions by seizing the Suez canal. This led to a war in which Iraq - a British ally - was compelled to participate. The final straw was the formation of the United Arab Republic between Egypt and Syria. Rather than joining it, the Hashemite regime of Iraq created a second Arab union with the Hashemite regime of Jordan. This was seen as British puppetmastering and led to a "Foreigners Out!" coup.
From this point, blaming the history of the region on any Colonial Power (except possibly the USSR, but even that is pretty iffy) becomes very difficult. The new leader backpedaled on joining the UAR on the insistence of the Iraqi Communist Party, greatly upsetting the pan-Arab nationalists, which was made worse (even if it proved the decision correct!) when the UAR collapsed because of severe differences between the two member countries a few years later. So the B'aathists spent a little time building power and launched a coup. After a few months of bloody purges, "Iraq first" and "Pan-Arabism" again led to violence, and the Pan-Arab portion of the government wound up purged and a new government formed. This government in turn would be overthrown by the B'aathists (bloodlessly this time) about five years later. There were a large number of claims of foreign plots to undermine the new government, with lots of executions, but little evidence has been found to substantiate these claims. It is very possible, even likely, that they were manufactured out of whole cloth to shore up the new government's stability.
After about ten years, Saddam took over, carried out the traditional purge, and went about his business. The path to the Gulf War started in 1980, when Saddam feared that Iran's Shia theocracy would foment an uprising among Iraq's Shia-majority population against the nominally secular and Sunni dominated government. Iraq's defeat in this ten-year conflict bankrupted the country and massively eroded the government's position. They couldn't even pay the troops on demobilization, and there's a pretty big risk involved in telling large numbers of armed men that they have to hand in their guns and get nothing for years of risking their lives.
But Iraq had a couple of very weak but very rich neighbors and a lot of armed men who'd spent years learning to fight. After interpreting a "I can't take a position on that" from the US ambssador as "That's your business, the US will not get involved" instead of "that's above my pay grade, I'll have to talk to Washington about their stance on this", they launched a Short Victorious War against Kuwait and Saudi Arabia. After several months of building up, this invasion was obliterated in Desert Storm with no mass civilian death or war crimes happening.
Putting all that down to "colonialism" is the same thing as saying "those brown people over their have no agency of their own, they're just mindless puppets doing whatever the Real People tell them to do".
As for your other example, nobody ever really claimed Vietnam was a "Just war". It was openly a "bail out the French fuckup, and hold the line against Communist influence". The tragic part, of course, is if the US government had been willing to tell the French to piss off, they could probably have Held The Line by simply investing in Ho Chi Minh - Vietnam was communist more because that's who was handing out weapons and support than for any other reason.