Many of those considered to be libertarians are not opposed to a powerful government in principle, just to pluralistic and democratic governments in particular. Not all libertarians are like this, some like Milton Friedman or PJ O'Rourke are entirely consistent in advancing liberty but others who don the mantle of libertarianism are nothing of the sort and are psuedo-libertarians at best.
Take the prominent US writer Lew Rockwell, who is generally associated with libertarianism and has a long term association with Ron Paul. Today he shares his deep thoughts on the Korean War:
When the Syngman Rhee regime in South Korea, which launched the war on the North in cahoots with the Truman regime here, also murdered at least 100,000 of its own people, with US supervision and approval. Truman's Air Force then drowned more than a million civilians in the North by deliberately bombing the dykes. Today, despite a militarist regime still supervised by US occupation forces, the South Korean people want peace, trade, and travel with the poor people of the North, no matter how rotten their socialist government. The US occupation prevents this. US Out! (Thanks to Ralph Raico and Antiwar.comIf he is aware of a single credible source that backs up the idea that it was South Korea that launched the war then he is keeping it to himself. At the start of the war the American and South Korean forces were so unprepared that the surprise attack managed to drive them all the way down the peninsular where they had to mount a desperate last stand just to cling on in Korea which makes no sense if they were the ones who launched an invasion. However rather than relying on reputable historians or using his brain, Rockwell prefers to simply parrot North Korean propaganda that is laughably dishonest. For someone who professes a distrust of all powerful states this is rather surprising behaviour.
It is true that Syngman Rhee was a despicable man who led a vile regime, but the fact that after just a few weeks of Communist rule most Koreans decided that he represented the lesser of two evils tells its own story.