Watching pirated or purchased content is one way. But most people would like to just stream content from the US, so I'll speak to that:
Currently the easiest mostly reliable way to bypass online content distributor restrictions on US content being viewed outside of the US is to use a DNS proxy that makes it appear as if one's DNS lookups originated from the US. I bought a lifetime subscription to such a service for just $30.
You can also use a VPN, but that is more difficult to set up, more costly, and not usually necessary.
However, the content distributors *could* block all non-US locations (except maybe Canada and Mexico) from receiving US content very effectively if they really wanted to do so due to one insurmountable fact: it takes a measurable amount of time for internet packets to travel the extra distance.
In Peru, for example, it takes a minimum of 13 ms for light to go from Peru to Miami. A round trip (sending a ping and receiving a response) will take a minimum of 26 ms. And that's a theoretical minimum if there are no intervening routers to slow things down even more, which there are.
I just pinged some servers in Florida and received times over 150 ms. Ouch! That's worse than I expected from my 100 Mbps internet connection!
If they really wanted to be draconian, they could do a ping test and only allow content to play for pings that are below a certain value.
There is no way this could possibly be evaded. In fact, I believe that HDCP (copy protection used by HDMI cables) already includes some time sensitive algorithms, so if you were to somehow transmit an HDCP protected HDMI signal a very long distance (like several miles) the algorithm would kick in, notice the response times between the player and TV are longer than they should be, and prevent it.
The online content distributors presumably don't already do this because (1) it isn't really that big of a problem for them at this point (2) it could negatively impact streaming to mobile devices which have higher latency (3) in some rare (high latency) cases it might prevent people in the US from streaming properly and (4) while not super difficult to implement, it wouldn't be entirely trivial and would cost a decent hunk of change.
But rest assured, if it became a widespread phenomenon that they really wanted to stop, they could do it.
However, I suspect that in the long run, geographically limiting content will become a thing of the past. While Netflix has recently become a bit more strict in detecting VPN usage (Hulu is currently the most strict), they've signaled to their content creators that they intend to push for geographic content neutrality in the future. As power shifts from the content creators to the online content distributors, I think this will eventually happen. Though I could, of course, be wrong (possibly the content creators could ultimately purchase and take over the online content distributors, for example).