Why doesn't military intervention in foreign conflicts work? Or does it?

Giving a people a hand up, yea. Even if they are former enemies. We have seen it work. Doing a half arsed job and then trying to placate factions that have been warring for hundreds if not thousands of years, not so much. If two parties want to kill one another only a fool stands in the middle. Especially if neither party especially likes the fool.

I think that a bigger mistake perhaps was not having a solid concrete plan in place for after the win. As SFC Mark Merino observed, the US Military is juggernaut not to be trifled with, but that can only do so much. When the politicians fail to have a plan in place for afterwards, they fail the troops. The military trains to be the hammer, and while they can do a lot to reach out and build friends, in the end, they can not be expected to be the velvet glove of diplomacy.

Lastly we need to understand the people, the culture and work within it, not try to mold it to our own. The Marshal plan didn't try to change the culture of the nations, just help them rebuild and extend the hand of friendship.

Since WWII, the US Military has been deployed without justified-reason, without a plan to bring the adventure into a fair, humane end game. Think of Korea, what did the US gain? Think of Vietnam? The, 'Domino Effect'? 56 thousand of our best, fell victim and another 21 hundred POW/MIA, WHY? The ungraceful retreat in 1975! Kissinger lurking in the background, pulling the strings! Millions of S. Vietnamese in, 'Re-Education Camps', tens of thousands perished at the sea trying to escape the Communist paradise that awaited them! Like the past decade, Iraq? We moved in to destroy a nation, based on false information, 'WMD's, mostly provided by our, 'friend', Zionist Israel and it's Agents, right here in the US, who are hidden in our Political System/AIPAC, et al. We destroyed, Libya, Afghanistan, Egypt, now working on Syria. Tens of millions of unfortunates are driven from their homes, hundreds of thousands are murdered, by the US and others, for Political and Religious Zealotry. The Continent of Europe is engulfed in a, 'Flood of Humanity' while tens of thousands perish while trying to get to a safe heaven. The US Military Might has been, 'Misused-Abused' for decades, The 'Blood and Treasure' of the People of the United States isn't sacrifised for the 'Safety and Security/Interest of the US. but for 'Foreign Entities'!!

The military never has and never will be able to build nations because it doesn't have the resources. That lies within governments that the United States has no jurisdiction over. The U.S. continues to waste an abundance of lives and money trying to police foreign nations under the direction of politicians who wouldn't dare risk anything and bear arms to defend this great nation. It' a sad testament that our nation's leaders stifle our military leaders and their ability to plan and execute decisive battles to win wars, but it's reality. I'm sure there are senior non-commissioned officers and junior field grade officers in war zones right now who were there very early in their careers at the beginning of this century. I honor their service and sacrifice, but only wish that our political leaders would allow our great military to cut the heads off of snakes instead of caging them like zookeepers.

It seems "Nation Building" is more of a tag line found in the showroom brochure use to sell whatever foreign entanglement our government is selling to the American people.
How would you feel if a foreign power ran roughshod through your neighborhood, after killing your kids, explaining they're there to help?

It is not the job of the Military to nation build as least it never has been before. The job of the Military is to go in kick ass and get the fuck out period.

Sp4 Byron Skinner. Simple answer sir, War Plans no longer define "Victory". We seek not territory, we don't want to destroy something like religious icons, we claim we are not in regime change but insist that who ever is in charge adopt a Capitalists, Democratic Republic. We don't demand it up front but only Christians may apply. We can't comprehend that most of the world is happy not being US. If you want to win wars you have to state what winning is.

I would like to answer that question with a question. If America became a failed state, how would Americans react if China came to intervene with a few hundred thousand Chinese troops? Once they establish control, the Chinese then completely revamp the American political structure, put curfews in effect in areas of unrest, and begin to manage the training of American police and military. I think we all know how that would turn out - about how Iraq, Afghanistan, etc. have been turning out when we try to intervene. Now, maybe if Canada stepped in to help put America back together things would work out but when you have the kind of cultural gap that exists between affluent, democratic, "Christian" America and a poor, dictatorial, Muslim country the stage is set for failure from the beginning.

Just like ALL problems, it's easier and cheaper to PREVENT the inequity. We shouldn't send in the troops until all the businessmen and diplomats have utterly failed to resolve the underlying problems that led to the conflict. Even then, killing bunches of people and breaking their economy is a productive solution in only the most extreme cases. It almost always leads to hatred and future revenge.

We are the most powerful military in the world. There is no mission anywhere that we can not complete, no objective left untaken. Having said that however, there is a big BUT and it is called Political insertion. Politicians, many of whom have never worn a uniform and many more who have, have never experienced deployments yet they set unrealistic and dangerous Terms of Engagement on those who are in harms way. Always, they are looking for ways to gain personally, be it votes or power, whatever.
Many years ago, when I was still on active duty, the average cost of training an enlisted man to competently perform his duties was approximately $300-350K or more. I have no idea of that cost today, but having spent all that money to train our seamen, soldiers and airmen, the taxpayer is being short changed all the way around.
POTUS, SECDEF, Senator X and Congressman Y have involved themselves in decision making, POAs, and every other aspect of the military fighting machine and by so doing have weakened our abilities to perform our missions. In Viet Nam we had Political action units whose sole function was to provide guidance and support to local political entities thus leaving the fighting units to complete their missions. The politicians have decided to spread the wealth, so to speak. Now all units are in the business of winning hearts and minds and it does not work. In the most recent past, our politicians seem to be bent on setting us up to fail, setting long term goals and then not giving us the time and resources to achieve them. Keep the politicians noses out of the military and We could get the job done, more than likely at far less cost and in far less time.

Mostly because at the end of the day the Military is run by pencil dick civilians. Then comes money, greed, special interest, political gain, back door deals, incompetence and the list goes on. The military is a broad sword, not a scalpel.