In Stephen King's it pennywise return and slumber was always signaled by some massive disaster. Like the shooting of the outlaw gang, the Kirchner ironworks, the death of George or the death of Adrian Mellon.
I have to wonder if king based that aspect of pennywise off people's habit of going crazy and just erupting into a wave of violence, hatred and hysteria every couple of years. (especially in America) the years king worked on the book IRL had the election then reelection of a republican president and Congress go back him him up, the second pinnacle of the cold war since the 50s. The lid portions of the book he based his own childhood on the 50s to the 60s had the start of the civil rights movement before it became full on political discord, the Vietnam War, almost every year from 62 to 68 someone in politics was assassinated or shot at.
My point is I guess every few years or generations there's always gonna be a cycle of violence that circles back around and defines an era. The 2010s ended with an election and a rise of political and social violence and the 2020s will forever be remembered as starting with more.