International libertarians tend to be really fascists, because they want to show that all that happens, when people are free, is that evil people take over and drive suffering. So, the only way to counterbalance the tendency of libertarianism to turn evil is to have a strong government put a stop to it.
They believe in such things as the Non-Aggression Principle and naive beliefs in the power of the "free" market. They want this for everyone, not just citizens of the US. Their ideology works best if every country is participating in free trade with free markets in both products and ideas.
If a critical mass of people were truly motivated by enlightened self-interest, then a global libertarian society might just be possible. However, this has never been the case and is very likely to never be the case.
There are some who claim that the current global neoliberal consensus is a form of libertarianism. The libertarians would disagree as they see too much taxation, regulation, and government control. However, socialists will look at this and say that the fact that a relatively small number of people control the vast majority of global wealth, and from this wealth they distribute mere crumbs among the world's poor and suffering masses is prima facie evidence that the libertarians have created their utopian paradise; at least those who made it to the top of the pyramid scheme.
I don't see how libertarianism has any relevance to fascism. Whatever bad can be said about libertarianism, it being fascist is not one of them. Also, I don't see that Nation A being libertarian would cause Nation B, or the world as a whole, to revert into fascism. Since there has never been a truly libertarian nation, there is no evidence to suggest such a link.
The word 'fascism' has lost all of its original meaning. It is mostly used as a synonym for bullying. I think some people will mistake libertarians for bullies because libertarians will tell someone on welfare to get off their butt and get a job. In this way some libertarians are misidentified as fascists just because they appear to the bleeding hearts as bullies.
Pragmatic "cafeteria style" libertarians can be allies with conservatives, especially since the US government and global agencies have grown far too large in size and power. However, true-blue libertarians are our enemies, and we should not seek to align ourselves with them.
One final thought: Adam Smith is hailed as being the first one to make a good case against mercantilism and in favor of free trade. However, things have changed drastically since his time. Since the invention of central heating and A/C, it is now possible to plant a factory in pretty much any country. Also, the current situation being a major exception, global supply chains make it relatively cheap and easy to move the inputs to production to wherever the cheapest labor and lowest regulation is located.
The idea that Nation A should limit itself to just those products and services that it is best at no longer makes sense. We were first told that raw material and food production is for suckers and developing nations because the ROI is too small and the price fluctuations too unpredictable. Then we were told that manufacturing was for suckers. The real money to be made was in the Financial Sector, i.e. the sector that generates no wealth except for the sector itself as it skims the profits of the producers of food, raw materials, and manufactured goods.
In such a world mercantilism starts to sound like a good option again, especially if we are blessed to live in a country like the US which has farmland, mines, energy supplies, places to locate factories, and people who could at least theoretically be properly educated. If most of our economy was buying and selling among ourselves then that might just work. We would pay higher prices for our goods and services because of higher salaries, but that could be paid for by excess production sold to other countries.