President Trump issued a stern warning to North Korea and words of reassurance to South Korea in a major speech Wednesday about his administration’s policy toward the Korean Peninsula.

“Today, I hope I speak not only for our countries, but for all civilized nations, when I say to the North: Do not underestimate us, and do not try us,” Trump said during a speech before the National Assembly in Seoul. “We will defend our common security, our shared prosperity, and our sacred liberty.”