There are many sites of significance from World War II on this island. I don't claim to be a history buff by any means but I'm learning bit by bit. There are two famous cliffs here, the Banzai Cliff and the Suicide Cliff, both of which were the locations of many deaths where Japanese soldiers leaped to their death rather than be captured or surrender once it was clear they could not hold the island.
This is the Korean Peace Memorial that sits somewhere near the base of Suicide Cliff, you can see the cliff in the background. The messages carved are of sorrow and condolence from Koreans to their fallen friends who had to die so far from their homeland.
Here's the wiki article of the Battle of Saipan if you are curious to know more history.