U.S. citizens and residents must pay tax on their worldwide income. There is a limited exclusion for earned income (up to $103,900 in 2018), but there is no exclusion for gain on the sale of property abroad.
A statutory term describing the cost used to determine your profit or loss from a sale or exchange of property. It is generally your original cost, increased by capital improvements, and decreased by depreciation, depletion, and other capital write-offs.