We're leaving Syria. GOOD. We're leaving Afghanistan. GOOD. The questions remain: what are US interests in either country? We don't have any strategic need to be in either country. Not any more.
And if the reason was "oil", that reason no longer exists. The US is now a net exporter of oil (https://www.bloomberg.com/news/articles/2018-12-06/u-s-becomes-a-net-oil-exporter-for-the-first-time-in-75-years). Unlike Europe, the US is no longer dependent on the Middle East for our petroleum products. We don't need to keep troops in the Middle East to "keep our oil flowing" over there.
If Germany, France, Spain, Belgium, and the rest of western Europe want to keep their oil coming, then it's time that they make the deals with the local governments in the Middle East. If they don't want Russia to be able to turn off its spigot and run Europe dry, then they need to send their troops to keep the oil flow coming. It's really simple: the US should militarily defend its interests without feeling obligated to militarily defend the interests of other countries.
That's "America First". We don't "stand alone" - but it's long past time for other countries to stand up and defend their own interests.
Mattis talked about the need for positive engagement with other countries, and he's right. Yes - the US should be a willing partner in mutual defense treaties. But those treaties should only relate to military attack. They shouldn't relate to economic issues. Yes, oil is a strategic asset - but each country should be responsible for independently obtaining its own strategic assets. The US shouldn't be solely responsible (or responsible in huge part) for defending access to other country's strategic assets.
But Mattis is a general, and a general wants an army. Trump's decision to bring troops home from Syria and Afghanistan was the opposite of what Mattis wanted to do and what his advisers (and too many hawkish neocons) wanted to do: keep the war machine going. It's too much like Vietnam: we can't really define the mission, but we know we need to keep fighting.
That's why I completely agree with and fully support Trump's decisions to reduce our troops in both Syria and Afghanistan, and possibly end our involvement in Syria. There will always be Islamic terrorism in the Middle East. It goes back centuries and won't end until Islamic leaders decide to end it. ISIS may be defeated, but some other group will crop up. Maybe a resurgent Al Qaeda. The Taliban. Whatever.
The mission in Afghanistan - capture or kill OBL - is over. Bring the troops home instead of leaving them there as targets. Enough have been killed already.
There was never a clearly-defined mission in Syria, other than to keep Assad from gassing his own people again and from invading Israel (again). Pull our troops out and bring them home. Leave Russia with the job of providing refuge to Syrian non-combatants who have been displaced by its (Russia's) actions. Israel is more than capable of standing off an attack from Syrian forces, and Russia won't attack Israel on Syria's behalf (it would put the US and Russia into direct conflict).
Bring the boys back home.