What war could the US start without the usual and immediate involvement of Russia, China or Iran -- I mean, except for a war with its own citizens that is.

The US lost the Afghanistan war, is slowly losing Irak to Iran, lost all face and is getting humiliated in Syria, failed at preventing Russia impose its presidential candidate, is alienating its european allies (see the Iran sanctions debacle), is supporting the savage Saudi Arabia -- who is losing the war in Yemen.

The US won Afghanistan handily, they just didn’t know what to do with it when they had it. I think America would have been better off placing Afghanistan under a military governor for a few years while they built up the country’s institutions.

Most powers make the same false assumptions that they "easily won" an insurgency/guerrilla war.

No you didn't win anything, you temporarily held territory, you wasted enormous resources, and were in fact beaten by goat herders in the end.

Without putting the whole country in a concentration camp and re-educating for 20 years and without providing an alternative economic model, a central administration in Afghanistan is irrelevant wether you do it for "a few year" or decades.

I think you’re conflating Afghanistan with Vietnam. America never fully committed to Afghanistan as they did with Vietnam. From the very outset they tried to do it on the cheap by relying heavily on the northern alliance. Subsequent to the invasion, America was far more interested in pursuing the Iraq war, so Afghanistan quickly became a backwater.

This meant that America became heavily reliant on local war lords (some of whom had dealings with the Taliban) to ensure security and maintain order. This undermined the government they were trying to build in Kabul and contributed to a culture of corruption. None of which endeared the common afghan to their newly formed institutions. The Taliban exploited these weaknesses with classic insurgency tactics and gradually took territory from the weak central authorities.

This was all entirely avoidable, America just didn’t stay focused on the mission.

IMHO, you should replace RF with Turkey. RF was unable to grab Ukraine or Georgia, which were completely unprepared to war.

RF completely achieved its objectives in Ukraine, Georgia and Syria, without putting a "we have won" show.

Sure, there are sanctions, because Russia actually annexed Crimea.

Russia knows very well that teritory grabbing in itself is pointless in the 21th century, Russia grabbed enough territory to nullify any chance Ukraine or Georgia will join NATO.

Don't get me wrong, as an eastern european, I hate what Russia stands for, but militarily and geostrategiclly, they know very well what they are doing, because they cannot aford not to, unlike the USA.