For the first time, more blacks are migrating to the United States from Africa than during the slave trade.

Since 1990, according to immigration figures, more arrived voluntarily than the total who disembarked in chains before the United States outlawed international slave trafficking in 1807. More have been migrating to the United States, with an addition of about 50,000 legal immigrants annually than in any of the peak years of the Middle Passage, the term commonly used for the trading route that once carried human cargo from West Africa to the Americas. In fact, since 1990, more blacks have migrated from Africa to the United States than in nearly the preceding two centuries.

New York State draws the most immigrants from Nigeria and Ghana, which are among the top 20 sources of immigrants to New York City, although many have moved to metropolitan areas including Washington D.C., Atlanta, Chicago, Los Angeles, Boston and Houston. Pockets of refugees, especially Somalis, have found havens in Minnesota, Maine and Oregon. Although the influx is still a trickle compared with the number of newcomers from Latin America and Asia, it is already redefining what it means to be African-American.

There has been a steady decline in the percentage of African Americans with ancestors who suffered directly through the Middle Passage and Jim Crow years, a period of severe and legal discrimination against blacks in the United States from the late 19th to the mid-20th century. This change in demography is shaping the debate over affirmative action, diversity programs and other initiatives intended to redress the legacy of slavery.

In Africa, the flow is contributing to a brain drain. But at the same time, African-born residents of the United States are sharing their relative prosperity by sending more than $1 billion back annually to their families and friends. “Basically people are coming to reclaim the wealth that’s been taken from their countries,” said Howard Dodson, director of the Schomburg Center for Research in Black Culture in New York City. The center has just inaugurated an exhibition, website and book titled “In Motion,” to commemorate the African Diaspora.

The influx has other potential implications, from recalibrating the largely monolithic way white America views blacks to raising concerns that American-born blacks will again be left behind.

“Historically, every immigrant group jumped over American- born blacks,” said Eric Foner, a historian from Columbia University in New York City. “The final irony would be if African immigrants did too.”

The influx from Africa began in the 1970s, mostly with refugees from Ethiopia and Somalia, and grew in the 1990s, when the number of black Americans born in sub-Saharan Africa nearly tripled. Combined with the much larger flow of Caribbean blacks, the recent arrivals from Africa accounted for about 25 percent of black population growth in the United States during the decade.

Nationally, the proportion of blacks who are foreign born rose to 7.3 percent from 4.9 percent in the 1990s. In New York City, about one in three blacks is born outside of the United States. The official numbers reflect only legal immigrants, who first arrived mostly as refugees and students and more recently through family reunification and diversity visas. Many speak English, were raised in large cities and capitalist economies, live in married-couple families and are generally more highly educated and have higher-paying jobs than American-born blacks.

There is no official count of the many who entered the country illegally or overstayed their visas and who are likely to be less well off. Kim Nichols, co-executive director of the African Services Committee, which directs newcomers to health care, housing and other services in New York, estimates there are at least four times as many illegal African immigrants as legal ones.

The immigrants arrive with their own perceptions and expectations, from countries where blacks constitute a majority at every level of society, only to discover that, whether they are professors or peddlers, they may be lumped together in the United States by whites and even by American-born blacks.

“That begs the larger question of what does it mean to have a black skin in the United States,” said Kathleen Newland, director of the Migration Policy Institute, a nonpartisan research group.

Agba Mangalabou, who arrived from Togo in 2002, recalled his surprise when he moved to the United States from Europe. “In Germany, everyone knew I was African,” he said. “Here, nobody knows if I’m African or American.”