“I was born in 1953. Like the rest of my generation, I took the America I grew up in for granted – in fact, like many in my generation I railed against the very real injustices of our society, marched against the bombing of Cambodia, went door to door for liberal candidates. It’s only in retrospect that the political and economic environment of my youth stands revealed as a paradise lost, an exceptional episode in our nation’s history.”

That’s the opening paragraph of my new book, The Conscience of a Liberal. It’s a book about what has happened to the America I grew up in and why, a story that I argue revolves around the politics and economics of inequality.

I’ve given this New York Times blog the same name, because the politics and economics of inequality will, I expect, be central to many of the blog posts – although I also expect to be posting on a lot of other issues, from health care to high-speed Internet access, from productivity to poll analysis. Many of the posts will be supplements to my regular columns; I’ll be using this space to present the kind of information I can’t provide on the printed page – especially charts and tables, which are crucial to the way I think about most of the issues I write about.

In fact, let me start this blog off with a chart that’s central to how I think about the big picture, the underlying story of what’s really going on in this country. The chart shows the share of the richest 10 percent of the American population in total income – an indicator that closely tracks many other measures of economic inequality – over the past 90 years, as estimated by the economists Thomas Piketty and Emmanuel Saez. I’ve added labels indicating four key periods. These are:

The Long Gilded Age: Historians generally say that the Gilded Age gave way to the Progressive Era around 1900. In many important ways, though, the Gilded Age continued right through to the New Deal. As far as we can tell, income remained about as unequally distributed as it had been the late 19th century – or as it is today. Public policy did little to limit extremes of wealth and poverty, mainly because the political dominance of the elite remained intact; the politics of the era, in which working Americans were divided by racial, religious, and cultural issues, have recognizable parallels with modern politics.

The Great Compression: The middle-class society I grew up in didn’t evolve gradually or automatically. It was created, in a remarkably short period of time, by FDR and the New Deal. As the chart shows, income inequality declined drastically from the late 1930s to the mid 1940s, with the rich losing ground while working Americans saw unprecedented gains. Economic historians call what happened the Great Compression, and it’s a seminal episode in American history.

Middle class America: That’s the country I grew up in. It was a society without extremes of wealth or poverty, a society of broadly shared prosperity, partly because strong unions, a high minimum wage, and a progressive tax system helped limit inequality. It was also a society in which political bipartisanship meant something: in spite of all the turmoil of Vietnam and the civil rights movement, in spite of the sinister machinations of Nixon and his henchmen, it was an era in which Democrats and Republicans agreed on basic values and could cooperate across party lines.

The great divergence: Since the late 1970s the America I knew has unraveled. We’re no longer a middle-class society, in which the benefits of economic growth are widely shared: between 1979 and 2005 the real income of the median household rose only 13 percent, but the income of the richest 0.1% of Americans rose 296 percent.

Most people assume that this rise in inequality was the result of impersonal forces, like technological change and globalization. But the great reduction of inequality that created middle-class America between 1935 and 1945 was driven by political change; I believe that politics has also played an important role in rising inequality since the 1970s. It’s important to know that no other advanced economy has seen a comparable surge in inequality – even the rising inequality of Thatcherite Britain was a faint echo of trends here.

On the political side, you might have expected rising inequality to produce a populist backlash. Instead, however, the era of rising inequality has also been the era of “movement conservatism,” the term both supporters and opponents use for the highly cohesive set of interlocking institutions that brought Ronald Reagan and Newt Gingrich to power, and reached its culmination, taking control of all three branches of the federal government, under George W. Bush. (Yes, Virginia, there is a vast right-wing conspiracy.)

Because of movement conservative political dominance, taxes on the rich have fallen, and the holes in the safety net have gotten bigger, even as inequality has soared. And the rise of movement conservatism is also at the heart of the bitter partisanship that characterizes politics today.

Why did this happen? Well, that’s a long story – in fact, I’ve written a whole book about it, and also about why I believe America is ready for a big change in direction.

For now, though, the important thing is to realize that the story of modern America is, in large part, the story of the fall and rise of inequality.