The hugely popular Uribe, who hands over power to Santos Aug. 7, has been battling armed drug overlords involved in the cocaine trail to the United States. Controversial military pacts with U.S. forces couldn't dislodge the guerrilla gangs that exert control over parts of Colombia.
Despite Uribe's exceptional achievements in turning the economy around and wresting control of much of the territory previously in the hands of FARC rebels, the ongoing conflict, narcotics traffic and urban crime remain top challenges for the incoming president, who won a clear majority in the second round of polling Sunday.
Much of the country's budget will continue to go into defense expenditure for an over-sized military machine and additional U.S. assistance will go into continuing the joint operations against the guerrillas, analysts said.
Santos received nearly 70 percent of the vote, against less than 30 percent for the
Green Party's Antanas Mockus, a former mayor of Bogota.
Much of the support for Santos came on the back of his endorsement by Uribe and a promise to create 2.5 million jobs.
In a victory speech, Santos made a strong call for national unity and promised to improve relations with neighbors, Ecuador and Venezuela, both of which oppose Colombia's close ties with the U.S. military.
Santos praised Uribe, whose approval ratings after eight years in office exceed 65 percent and promised to build on his success.
"This is your triumph, too, President Uribe," he said. "We'll build on the progress you achieved over the past eight years. Thanks to the security we've created, we can now focus on creating jobs, fighting poverty and providing opportunities for all Colombians," said Santos.
He echoed Uribe's hard line on "no negotiation" with the FARC rebel group and warned he would continue Uribe's tough military campaign to secure the release of all hostages. The numbers of people held by FARC remain uncertain.
Santos led tough campaigns against FARC when he served as defense minister from 2006 to 2008.
Mockus offered Santos conditional support, saying he would support "the good things" of the Santos administration but wouldn't hesitate to condemn the "bad things."
He said the opposition wouldn't tolerate any illegal actions by the government.
The balloting in the second round Sunday was guarded by security forces but early reports said Election Day violence killed at least seven government troops and 10 insurgents.
Officials attributed low turnout to the World Cup as many people stayed indoors to watch the tournaments. Analysts said security fears in outlying areas had kept many people away.