I'm Peter Roberts, immigration attorney who does work for YC and startups. AMA

EU citizens don't need a passport to travel across the EU (even outside the Schengen area, where you have to go through a border check), they just need an identity card.

(most) EU citizens could also travel to Turkey with their identity card.

EU citizens could travel to the UK with their identity card, for a few years after Brexit, as long as they got UK (pre-)settled status.

Russian citizens can travel to Armenia, Belarus, Kazakhstan, and Kyrgyzstan without their international passport. They instead have an "internal" passport (meant to be used like an identity card, and for travel to closed towns inside the country), which is recognised by those other countries.

The same applies in the other direction for citizens of nearby countries travelling to Russia (even in the case of an Abkhazian internal passport. Abkhazia is recognised by only ~6 other UN member states).

I'm not sure in which way a US "passport card" differs from a plastic identity card. But it's notable that a few countries don't have either (UK doesn't... Russia and a few neighbouring countries, as mentioned before, instead have an "internal passport")

Of course, something in common with all the examples above, and with US citizens travelling to Mexico, is that you're travelling to neighbouring countries with friendly relations.

US simply doesn't have any official identity card.

So they make up replacements for when it's convenient to actually have one.

I suppose the goal is to encourage innovation in the identity theft industry... after all it adds to the PIB doesn't it?

When I have traveling within the US I never take my passport. There is zero need and I may lose it so why even bother taking it when it serves no use?

My trip was a 6 week long road trip from the south eastern US through Texas, New Mexico, Arizona, California, up to Seattle in the northwest, and then back to the south eastern US.

I had no intention of going to Mexico or Canada. They are fine countries but that was no the intent of this trip so I left my passport at home.

During this trip I learned that the US border patrol has set up border inspection points about 10 to 50 miles inside the US. Most of the southern border are remote desert regions where people can cross on foot and then try to meet up with someone in a vehicle on the other side. So the border patrol doesn't just patrol the actual border but has checkpoints inside the US on the roads near the border.

You don't need a passport to get through these as you never left the country.

But I was driving a vehicle (Honda CR-V) with an open cargo area that showed it was full of luggage, bags of food, and lots of water bottles. I probably looked suspicious like I was picking up immigrants on foot or smuggling drugs.

I wasn't. I was on a big road trip and wanted to be prepared for days if my car broke down on a side road and I was stuck in a desert area waiting 3 days to be rescued.

Militarily speaking, yes. But unlike the other examples, there is a huge economic difference between the US and Mexico, meaning migration flows exclusively one way. Illegal crossings are extremely common and the US has strong incentives to prevent them. It's hard to compare the US-Mexico border to any other border in the world.

But they have a "passport card"

https://www.citizensinformation.ie/en/travel-and-recreation/...

I don't see why Bundespolizie would have had to treat people differently, alas it's usually difficult to argue with a foreign country border police