What country was once a fierce enemy, but is now one of your closest allies?

Korea

Not exactly an ally, but Mongolia invaded us 800 years ago, and now is one of Korea’s major markets and closest partners.

Also the US and France initially were invaders in the late 1800s, while countries like Germany and the UK all partially joined in the conquest for Korea. Nowadays the US is an official ally, and all other countries are our close friends.

nhân dân ta ca muôn năm
hồ tập chương mao trạch đông @Joker_checker