Josiah had put the temple in order. After all of that, Neco went up to fight at Carchemish. He was king of Egypt. Carchemish was on the Euphrates River. Josiah marched out to meet Neco in battle.
References for 2 Chronicles 35:20
But Neco sent messengers to him. They said, "King Josiah, there isn't any trouble between you and me. I'm not attacking you at this time. I'm at war with another country. God told me to hurry. He's with me. So stop opposing him. If you don't, he'll destroy you."
But Josiah wouldn't turn away from Neco. He wore different clothes so people wouldn't recognize him. He wanted to go to war against Neco. He wouldn't listen to what God had commanded Neco to say. Instead, he went out to fight him on the flatlands of Megiddo.
Men who had bows shot arrows at King Josiah. After he was hit, he told his officers, "Take me away. I'm badly wounded."
So they took him out of his chariot. They put him in his other chariot. They brought him to Jerusalem. There he died. His body was buried in the tombs of his family. All of the people of Judah and Jerusalem sobbed over him.