WASHINGTON -- On Tuesday, July 11, the United States will become more geographically stable than it has ever been. It will have been 17,126 days since the admission of Hawaii to statehood on Aug. 21, 1959. The longest previous span between expansions of the nation was the 17,125 days between the admission of Arizona on Feb. 14, 1912, and the admission of Alaska on Jan. 3, 1959. Since then the nation has become, in a sense, smaller through the annihilation of distance and, to some extent, of difference.

An important part of the groundwork -- literally, it covered a lot of ground -- for today's America was begun 50 years ago this summer. A conservative Republican president, who grew up in a Kansas town where hitching posts for horses lined unpaved streets, launched what was, and remains, the largest public works project in the nation's history -- the Interstate Highway System. Its ribbons of concrete represent a single thread of continuity through the nation's history.

With that program, Dwight Eisenhower, the 13th Republican president, helped heal the wounds of the war won by another general, U.S. Grant, the second Republican president. That war was related to ``internal improvements,'' as infrastructure projects such as roads and canals used to be called.

In 1816, South Carolina's Rep. John Calhoun -- then a nationalist; later, a disunionist -- introduced legislation for a federal program of internal improvements. The legislation passed but President James Madison vetoed it because he thought Congress was not constitutionally empowered to do such things. So, prosperous Northern states built their own improvements while the South sank into inferiority and increasing dependence on slavery.

The military handicap of an inferior transportation system was one reason the South lost the Civil War. Another reason was the industrialization of the North. Its transportation system (the Erie Canal, railroads) cut the price of shipping a ton of wheat from Buffalo to New York City from $100 to $10, and the difference between the wholesale price of pork in Cincinnati and New York plunged from $9.53 to $1.18. Suddenly, workers flooding into the North's cities had more disposable income to spend on the North's manufactured goods.

The first Republican president began his public life as a 23-year-old candidate for the Illinois General Assembly by telling voters of Sangamon County his ``sentiments with regard to local affairs,'' the first sentiment being ``the public utility of internal improvements.'' The vigor of the union also was a preoccupation of Teddy Roosevelt, the eighth Republican president, whose great internal improvement, the Panama Canal, was external, although he thought of Panama as America's private property. And Eisenhower's message to Congress advocating the IHS began, ``Our unity as a nation is sustained by free communication of thought and by easy transportation of people and goods.''

No legislator more ardently supported the IHS than the Tennessee Democrat who was chairman of the Senate Public Works subcommittee on roads. His state had benefited handsomely from the greatest federal public works project of the pre-war period, the Tennessee Valley Authority, which, by bringing electrification to a large swath of the South, accelerated the closing of the regional development gap that had stubbornly persisted since the Civil War. This senator who did so much to put postwar America on roads suitable to bigger, more powerful cars was Al Gore Sr. His son may consider this marriage of concrete and the internal combustion engine sinful, but Tennessee's per capita income, which was just 70 percent of the national average in 1956, today is 90 percent.

The IHS -- combined, as Fortune magazine's Justin Fox writes, with another bright idea from 1956, the shipping container -- made America's distribution system more flexible. This benefited manufacturers, foreign and domestic, especially in America's hitherto lagging region, the South. This is one reason there is a thriving Southern-based automobile industry (BMW in South Carolina; Mercedes in Alabama; Honda in both Carolinas, Georgia and Alabama; Toyota in Tennessee, Alabama and Kentucky). Furthermore, the South is home to some of today's ``big box'' retailers -- Wal-Mart (Bentonville, Ark.), Home Depot (Atlanta) -- as well as FedEx (Memphis).

American scolds blame the IHS and the automobile for everything from obesity (fried food at every interchange) to desperate housewives (isolated in distant suburbs without sidewalks). Nikita Khrushchev, during his 1959 visit to America, told Eisenhower, ``Your people do not seem to like the place where they live and always want to be on the move going someplace else.'' Eisenhower knew that wherever people are going on their nation's roads, they are going where they live.