WASHINGTON — To glimpse how migration is changing the world, consider Western Union, a fixture of American lore that went bankrupt selling telegrams at the dawn of the Internet age but now earns nearly $1 billion a year helping poor migrants across the globe send money home.

Migration is so central to Western Union that forecasts of border movements drive the company's stock. Its researchers outpace the Census Bureau in tracking migrant locations. Long synonymous with Morse code, the company now advertises in Tagalog and Twi and runs promotions for holidays as obscure as Phagwa and Fiji Day. Its executives hail migrants as "heroes" and once tried to oust Rep. Tom Tancredo, R-Colo., because of his push for tougher immigration laws.

"Global migration is the cornerstone of how we've grown," said Christina A. Gold, Western Union's chief executive.

With five times as many locations worldwide as McDonald's, Starbucks, Burger King and Wal-Mart combined, Western Union is the lone behemoth among hundreds of money transfer companies. Little noticed by the public and seldom studied by scholars, these businesses form the infrastructure of global migration, a force remaking economics, politics and cultures across the world.

Last year, migrants from poor countries sent home $300 billion, more than three times the world's foreign-aid budgets combined.

Western Union's dominance of the industry casts it in a host of unlikely new roles: as a force in development economics, a player in U.S. immigration debates and a target of contrasting attacks.

Its unparalleled reach gives millions of migrants a safe way to transmit money, and may even increase the amounts sent. But critics have long complained about its fees, which can run from about 4 percent to 20 percent or more. And the company's lobbying for immigrant-friendly laws has raised the ire of people who say it profits from, or even promotes, illegal immigration.

Western Union tracks migrants so closely that it has made pitches to illegal immigrants just released from detention camps.

After settling a damaging lawsuit that accused it of hiding large fees, Western Union set out to recast its image, portraying itself as the migrants' trusted friend. Over the past four years, it has spent more than $1 billion on marketing, selectively cut prices and charged into American politics, donating to immigrants' rights groups and advocating a path to legalization for illegal immigrants.

While some migrant groups remain wary, the company has won unlikely praise.

"Western Union has become a company that values and protects its customers," said Matthew J. Piers, the Chicago lawyer who sued the company. "Nobody was more surprised at the change than me, because I was Western Union critic Numero Uno."