The International Date Line can be anywhere on the globe.
But it is most convenient to be 180° away from the defining meridian that goes through Greenwich, England.
Over the years, the position of the International Date Line has changed several times.
Until 1845, the Philippines were on the eastern side of it (the same side as the United States).
It was on the eastern side of the line because it was a Spanish colony and most Europeans arrived there via the Spanish colonies in South America.