A borderline that for generations was like a picket fence between neighbors is now a wedge between old friends.

At legal entry points along the U.S.-Mexico border, lines of cars often stretch for blocks as people wait to cross into and out of Mexico. Between the ports, most flimsy, barbed-wire cattle fences have been replaced by hulking steel walls or chest-high vehicle barriers made of railroad ties.

It's tougher than ever to cross, legally or illegally. And that has altered the borderlands for people who live, visit, ranch or own businesses there.

The transformation can be traced to several changes over the last two decades:

• A mid-1990s security push beefed up enforcement in Texas and California, funneling smuggling of people and drugs into Southern Arizona. The idea was that the harsh desert and deadly heat would be a natural deterrent. It wasn't, and Arizona has been the border's busiest smuggling corridor since the late 1990s.

• The terrorist attacks of Sept. 11, 2001, shifted the nation's focus to homeland security. Lines into the U.S. grew as customs officers faced increased pressure to keep terrorists from entering the country.

• As illegal immigrants put down roots rather than cross back and forth, the illegal immigrant population in the U.S. swelled to 10 million-plus in the mid-2000s. A historic buildup of agents, fences, roads, highway checkpoints and technology followed. Five times the number of Border Patrol agents now work the Southwest border than in 1992. The parent agency's nearly $12 billion budget is double what it was the first year after Homeland Security was created in 2004.

• In early 2007, newly elected Mexican President Felipe Calderón launched a crackdown on Mexican drug smuggling organizations that led to an era of bloodshed. Pinched by the pressure, cartels warred for prized corridors and against government forces trying to weaken them. As drug-related murders spiked, security fears cut into visits by Americans to Mexico and sparked U.S. State Department travel warnings for Mexico.

• In 2009 the Obama administration escalated checks of vehicles and people leaving the U.S. for Mexico, trying to stop the flow of guns, ammo and cash that fuel the cartels.

• In March 2010, Cochise County rancher Robert Krentz was found slain on his ranch northeast of Douglas. The case remains unsolved, but it's suspected he was killed by a smuggler. Many say the event helped Gov. Jan Brewer pass Arizona's tough new immigration law, SB 1070, a few months later.

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Because of all these changes, ports of entry that used to feel like rotating gates monitored by security guards are now hardened checkpoints. In addition to border walls and fences, wide dirt roads run parallel on much of the U.S. side, with lights and camera towers in urban areas.

Mountains, valleys and canyons that were a playground for hikers, birders and hunters have been scarred by illegal border crossers and the federal agents chasing them. Ranchers who used to tip their hats to illegal border crossers now carry high-powered rifles, fearful of possible encounters with smugglers.

The borderlands remain home to thousands who still live rich lives there - but some of what made them so special before is gone, probably forever.

Contact reporter Brady McCombs at 573-4213 or bmccombs@azstarnet.com