ABOARD A P-3 ORION, over the Pacific Ocean — The Department of Homeland Security is increasingly going global.

An estimated 2,000 Homeland Security employees — from Immigration and Customs Enforcement special agents to Transportation Security Administration officials — now are deployed to more than 70 countries around the world.

Hundreds more are either at sea for weeks at a time aboard Coast Guard ships, or patrolling the skies in surveillance planes above the eastern Pacific Ocean and the Caribbean Sea.

The expansion has created tensions with some European countries who say that the United States is trying to export its immigration laws to their territory. But other allies agree with the United States’ argument that its longer reach strengthens international security while preventing a terrorist attack, drug shipment, or human smuggling ring from reaching American soil.