Many other rich countries give more on a per capita basis.[1]
Indeed the U.S. has been kinda cheap, on a percent of gross national income basis.[2]
It could be countered, of course, that the U.S. has paid substantially more for defense, and for the defense of many donor countries.
This data only includes government spending, which leaves out private and NGO spending. Many Americans prefer that their charity funds be spent outside of the control of the government.