The U.S. B-1/ B-2 visa validity is dependent on what kind of passport a person is holding.
Citizens of some countries are eligible for longer B-1/ B-2 visa validity than other countries. For example, citizens from the Philippines, Thailand, Indonesia, and China are eligible to receive a B-1/B-2 visa valid for up to 120 months (a 10 year multiple-entry visa). After 10 years, citizens of those countries are required to apply for a new visa. Vietnamese citizens and other South East Asian countries, however, are only eligible to receive multiple-entry B-1/B-2 visas for up to one year, while Cambodian citizens are limited to a double-entry B-1/B-2 visa for a maximum of three months.
Overall visa validity is determined by the U.S. Department of State which bases its determination on the “reciprocity schedule”. According to the Department of State, the principle of reciprocity occurs when a foreign government imposes fees or visa validity restrictions on U.S. citizens for certain types of visas, and the United States will impose a reciprocal fee or validity on citizens of those countries for similar types of visas.
More information on reciprocity can be found at https://travel.state.gov/content/travel/en/us-visas/Visa-Reciprocity-and-Civil-Documents-by-Country.html.
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