New data released today by the U.S. Census Bureau show the largest increase in poverty in U.S. recorded history. Under President Obama’s watch, an additional 3.7 million Americans fell into poverty in 2009.

Buried in the Census report are startling figures revealing the principal cause of child poverty: the collapse of marriage. Single mother families are almost five times more likely to be poor than are married couples with children; overall, nearly 70 percent of poor families with children are headed by single parents.

The big secret in the Census report is that marriage is America’s number-one weapon against child poverty. But marriage has been rapidly declining in our society as the number of women who have children without being married has skyrocketed.

Historically, unwed childbearing was rare. In 1964, when the federal government launched its War on Poverty, 6.8 percent of births were to single mothers. Today, the unwed birth rate has soared to 40 percent: four of every 10 births are to a single mother. For Hispanics and African Americans, it’s significantly higher.

This trend is extremely detrimental for society. When compared to children raised by married parents, children raised by single parents are more likely to have emotional and behavioral problems; be physically abused; smoke, drink, and use drugs; be aggressive; engage in violent delinquent and criminal behavior; have poor school performance; and drop out of school.

Contrary to conventional wisdom, nearly all unwed fathers are employed, and most earn enough to lift mother and child from poverty. Tragically, however, few unwed parents marry.

Many commentators will say teen pregnancy accounts for most single motherhood, but this is false. Less than 8 percent of new single moms are under 18. In fact, most unwed births are to young adult women in their 20s. The majority of unwed moms don’t have much education; most end up on welfare.

If Americans are serious about reducing poverty and getting control of federal welfare spending, we must strengthen marriage. We can do this in several ways, beginning with reducing anti-marriage penalties currently in welfare programs and providing factual information to low-income communities about the benefits of marriage.