It could be disputes over oil, its relationship with Iran, the support of nefarious factions, or all the above. What is certain, is that the relationship between the US and Iran is strained, to say the least. And the truth is, since the 1979–81 Iran hostage crisis, things have never been the same between the two countries.
The conflict between Syria and the US didn't begin as a Syrian - US conflict, but as a Syrian civil war. Needless to say, once the US stepped in two help, all bets were off for an amicable relationship.
There has been tension, war, and distrust between the US and Iran for decades. The Gulf War in the 1990s, the invasion of Kuwait, and other notable events have made Iran one of the top US enemy countries.
The relationship between Libya and the US has made marginal gains, but there is still a long way to go. The top reason Libya is perceived as one of the potential US enemy countries is its ties to terrorism, which led to targeted US bombing in the mid-1980s.
While Somalia as a whole may not be considered one of the top US enemy countries, the terrorist factions within its borders keep it on the radar. That has also led to US military operations in Somalia as a part of counter-terrorism efforts.
The US relationship with Pakistan has been rocky, with a history of ups and downs. Due to its continued ties, interactions and affiliations, there remains a level of distrust in the motives and goals of the Pakistan nation.
Historically, Russia has always been one of the top US enemy countries. The conflicts between the two powers in both World Wars I and II have become that of historical record and lore. Currently, that unsettled relationship between the two powers has raised its head again with the Russian invasion of Ukraine.
Another US enemy country that needs little introduction is North Korea. The conflict and discord between the US and North Korea is well-documented, and not much of a secret to anyone. This is also another one of those US enemy countries that has a long history of bad blood and spilled blood.
While Mexico wouldn't be considered a traditional US enemy country, it's proximity to the US, and its pipeline of terrorism and drugs into America make it a threat.
The top enemies of the United States include China, Russia, Iraq, North Korea, Afghanistan, Pakistan, Venezuela, Yemen, Syria, and Belarus.