The island of Guam

Postcard
The card shows a picture of the entire island of Guam from 13,000 feet (4000 Km) showing the Earth's horizon on a perfectly clear day.

The text on the card reads "Guam Micronesia". Here Micronesia refers to the overall region, not the country. Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. Micronesia is divided politically among several sovereign countries. One of these is the Federated States of Micronesia, which is often called "Micronesia" for short and is not to be confused with the overall region.

Stamp
The postmark reads Barrigada. This is the post office located near/at the airport.