"The first debt limit was established to give the Treasury autonomy over borrowing by allowing it to issue debt up to the ceiling without congressional approval, making it easier to finance mobilization efforts in World War I. Before that, Congress generally had to authorize the Treasury to borrow in smaller increments."

So what's different now? Welll...

"In the last two decades, the U.S. has added $25 trillion in debt, spending nearly $1 trillion more than it receives in taxes and other revenue every year since 2001—in large part due to financing wars, tax cuts, emergency responses, and expanded federal spending. To make up the difference, the government has to borrow money to continue to finance payments that Congress has already authorized."

A large part of that spend were the wars in Afghanistan and Iraq. Under President Bush, the war spending was "off budget". In other words, it was funded by emergency spending declarations. $1.1 trillion in direct costs and $2.4 trillion in indirect costs and interest.