April 15 is the most important day on the North Korean calendar — it’s the birthday of the founder of North Korea, officially known as the “Day of the Sun.”

This year, experts and analysts warn that North Korean leader Kim Jong Un might use the day as an excuse for a dramatic show of force. As my colleague Anna Fifield reported:

Expectations remain high that North Korea will conduct another nuclear or missile test, or carry out some other incendiary act, to mark the most important day on its calendar: the anniversary Saturday of the birthday of Kim Il Sung, the country’s founder and the current leader’s grandfather.

In recent days, the North Korean army has threatened to annihilate U.S. military bases in South Korea in response to what it called President Trump’s “maniacal military provocations.” In response, the Trump administration warned that all options are on the table. The United States has sent an aircraft carrier strike group to the Korean Peninsula region. Trump has tweeted that the United States will act against the country, with China or independently. It’s gotten so contentious that China has publicly chastised both countries and asked them to chill.