Even if you are clueless about the international arms trade - South Korea has maintained a huge military for the past 70-ish years, as part of their endless cold war with North Korea. And South Korea has been really big on manufacturing and exporting all sorts of stuff for the past half-ish-century. Why the hell wouldn't they be selling the military things that they are building anyway, at scale, to any and every non-enemy with money to spend?
HN guidelines typically prefer sourcing a title from the text of the document itself. Given Politico seem to be rotating through clickbait variants (the presently displayed title is "Trump Is Tired of Arming Allies. This Country Is Stepping Up.", the submitted title appears elsewhere in the page source), I'd suggest:
"The rise of South Korea’s weapons business"
Which is non-clickbaity, succinct, clear, and accurate. It appears at the start of the 4th body 'graph.
I'd argue it's superior to the subtitle "The U.S. retreat from the global stage is an opportunity for South Korea.", as that option fails to indicate the nature of that opportunity. South Korea and arms trade are the key elements discussed.