1995: The flow of illegal immigrants and marijuana across Arizona's border spikes after a push to boost enforcement in Texas and California.
2000: The Border Patrol's Tucson Sector registers 616,346 apprehensions - the second-most ever made in a Southwestern border sector.
Sept. 11, 2001: Terrorist attacks shift the nation's focus to securing its border, leading to more stringent checks and longer lines into the U.S.
March 1, 2003 : In response to the 2001 terrorist attacks, the Department of Homeland Security is created, absorbing the Immigration and Naturalization Service and taking control of border security.
April 2006: President Bush sends 6,000 National Guard troops to the border in two-year mission and calls for 6,000 more Border Patrol agents by 2008.
2007: Newly elected Mexican President Felipe Calderón decides to crack down on drug smuggling organizations. The cartels begin to battle for power and against the government, and drug murders spike.
2009: Law enforcement agencies in Arizona seize a record 1.6 million pounds of marijuana, 1.2 million of which is stopped by the Border Patrol.
2009: Passports become mandatory for U.S. citizens re-entering the country. The Obama administration begins checking people and vehicles leaving the U.S. for Mexico for guns, ammo and cash that fuel cartels.
March 2010: The killing of Cochise County rancher Robert Krentz brings a renewed focus on the safety of border residents.