Danielle Allen

is a professor of social science at the Institute for Advanced Study in Princeton

In Hopewell Township, the veterans of American Legion Post 339 have put their building up for sale. The post is down from 425 paying members in the 1960s and '70s to 202 this year; about a dozen regularly attend.

But it's America that has changed, not vets.

Since 1970, the U.S. population has grown by about 50 percent, from roughly 200 million to 300 million. Over the same period, the number of active-duty armed forces has fallen about 50 percent, from 3 million to 1.4 million. A far smaller percentage of the citizenry now serves in the military.

In 1969, 13 percent of Americans were veterans; in 2007, 8 percent were.

Even more important than demographic shifts is the change wrought by the end of the draft in 1973. Until then, military service was distributed pretty evenly across regions. That is no longer true. The residential patterns for current veterans and the patterns of state-level contributions of recruits to the all-volunteer military have a distinct geographic tilt. Tellingly, the map of military service since 1973 aligns closely with electoral maps distinguishing red from blue states.

In 1969, the 10 states with the highest percentage of veterans were, in order: Wyoming, Pennsylvania, West Virginia, California, Oregon, New Jersey, Massachusetts, Ohio, Connecticut and Illinois.

In 2007, the 10 states with the highest percentage of post-Vietnam-era veterans were, in order: Alaska, Virginia, Hawaii, Washington, Wyoming, Maine, South Carolina, Montana, Maryland and Georgia.

Which states have disappeared from the top 10? California, New Jersey, Massachusetts and Illinois, all states that have voted Democratic in the past five presidential elections. These states and New York are among the 10 states with the lowest number of post-Vietnam vets per capita. New Jersey comes in 50th, with 1 percent of its residents having served in the military since Vietnam.

This is not simply an issue of people retiring to warm states. A 2005 Heritage Foundation study found that Montana, Alaska, Florida, Wyoming, Maine and Texas send the most young people per capita to the military. The states with the lowest contribution rates? Rhode Island, Massachusetts, Connecticut, New Jersey and New York.

What's clear is that a major national institution, the U.S. military, now has tighter connections to some regions of the country than others.

We can't treat the uneven pattern of military service as an insignificant reflection of the cultural differences that characterize different regions of this diverse country. Military institutions across nations and throughout time have always been important creators of culture. They strive to develop unbreakable bonds of solidarity among their members based on shared values, experiences and outlooks. The U.S. military's leadership role in racial integration has been understood in just this way.

If young people from different regions and social backgrounds either enter or steer clear of the armed forces, military service will become, over time, an experience that doesn't ease but exacerbates cultural differences. Is the all-volunteer military already having this effect?

It is time to think about a structure for national service - military and non-military - that could integrate young people from different regions of the country so that they will come, at least, to understand each other. We need to weave a fabric of shared citizenship anew.

This article originally appeared in the Washington Post.