[NJ_gent]

"Not true, taking up arms in a foreign military can lose you your citizenship."

Joining the military or voting in an election in a foreign nation may be construed as a renunciation of citizenship. The United States government is incapable of revoking your citizenship against your will except in cases of naturalization involving fraud. You must, by overt and unambiguous action, renounce your claim to US citizenship to lose it. Even making war against the United States is not necessarily grounds for losing citizenship.

See here for more.

[ndt]

"Joining the military or voting in an election in a foreign nation may be construed as a renunciation of citizenship."

You are correct in that there needs to be an intention on the part of the person to relinquish it. While a good argument could be made that it is inherent in the act of waging war with a foreign military against the U.S. Barring a formal declaration of renunciation by the citizen, proving intent in this case would be very high bar.

from INA Sec. 349. [8 U.S.C. 1481]
"A person who is a national of the United States whether by birth or naturalization, shall lose his nationality by voluntarily performing any of the following acts with the intention of relinquishing United States nationality- "

P.S. Great arguments, I'm glad to see you.