How long till the US army runs out of refined oil though ? How long till the tech seeps into the local people and gets turned around guerilla-style ? Logistics are what win or lose an invasion. Interstellar logistics are pretty much impossible barring any sort of "stargate" technology.
(Also, Napoleon era tech already included rifles with near-semiauto fire capability and decent clip size, like the Girandoni Windbüchse used by the Tyrolian elite soldiers of the Austrian army.)
Then I wondered what an alian would look like to me, a human. I decided that an alien would look just like another human. So I began to wonder what advanced characteristics I couild watch out for. Successful businessman, good luck, healthy long life, mysterious origin, that sort of thing.
The best example individual that fits, is Elon Musk. The guy is ridiculously successful, but that is merely a means to his alien ends, which seem to be: to go back to his home planet. He needs processing power, so he funds high tech development, then sells it when it's sufficiently advanced so he can focus on developping the battery tech that he will also need later on, etc. Repeat the cycle until he gets the effective rocket / spaceship / dimensional portal tech required to get back home.
The Macintosh is Xerox technology at its best.