Oh it can be conquered.......but you are dealing with a bully religion/culture.......so being a nice guy and doing nation building isn't how it will be conquered. They only respect the sword and see kindness as a weakness and invitation to attack.
The thing is, there was a way to have settled the country down quickly.
Mohammed Zahir Shah was the last "King of Afghanistan", and very popular. He was their king, until his cousin staged a coup and he was forced into exile. When the Taliban was deposed, the Afghan government named him "Father of the Country", and gave him a lifetime pension. But he was forced to make concessions in order to be allowed to return to Afghanistan, where he renounced throne.
If the State Department was smart, they would have restored the monarchy, and used it to restore stability and given the people a popular figure to rally around. Set up a modern Constitutional Monarchy, then start the process of moving them into a Republic. After a period of a few decades.
But no, they were so obsessed on "democracy", that none of them thought about what it meant. Especially when such a nation never had that in their entire history. To them, it meant "mob rule", and the ones that had the most voted ruled over everybody else. And ultimately, the same thing as has happened in Iraq. A failed government, and the Diplomats looking at each other and wondering why it failed.
The only real examples in the last century of a successful transition almost always resulted form a strong dictator, who then towards the end set up the foundation to form a Republic after they died. Franco did that in Spain, and Chiang Kai-shek did that in Taiwan. However, even that will not always work, as we all learned in watching Yugoslavia implode after Marshal Tito died. But so long as the processes are established and being followed, it seems to greatly enhance the odds that the country will pass into a Republic rule, in time.
