Original: Between 1668 and 1815, Guam was an important resting stop for the Spanish Manila galleons, a fleet that covered the Pacific trade route between Acapulco (Mexico) and Manila (Philippines). Guam, along with the rest of the Mariana and Caroline Islands, were treated as part of Spain's colony in the Philippines.
Simplified: Spain took over Guam in 1668, and it was an important place for Spanish delivery boats every year going between Mexico and the Philippines, known as the Manila Galleon.