Legality of battle advice to non American military
<p>Is it legal to directly <strong>advise or become advisor</strong> to a military in a war in which America is neutral?</p>
<p>Would the act itself be punishable by loss of citizenship?</p>

<p><a href="https://www.law.cornell.edu/uscode/text/18/960" rel="nofollow noreferrer">18 USC 960</a> provides a disincentive against such actions.</p>
<blockquote>
<p>Whoever, within the United States, knowingly begins or sets on foot or
provides or prepares a means for or furnishes the money for, or takes
part in, any military or naval expedition or enterprise to be carried
on from thence against the territory or dominion of any foreign prince
or state, or of any colony, district, or people with whom the United
States is at peace, shall be fined under this title or imprisoned not
more than three years, or both</p>
</blockquote>
<p>Also see <a href="https://www.law.cornell.edu/uscode/text/18/959" rel="nofollow noreferrer">18 USC 959</a>, covering enlistment. &quot;At peace&quot; is not statutorily defined, so it is not obvious whether the US is &quot;at peace&quot; with Ethiopia (Tigray war) or Russia (various offenses). A formal state of war has not existed between the US and another nation for 70 years.</p>

<p>Partial answer:</p>
<blockquote>
<p>Would the act itself be punishable by loss of citizenship?</p>
</blockquote>
<p>No. This is not an activity for which U.S. citizenship can be revoked.</p>

united-states citizenship military mercenary