The former Colombian hostage visited eight nations this past week pushing for leaders to support efforts to free hostages still held by leftist rebels.
Business elites and conservative governments worry about his opposition to free-trade deals.
The head of Colombia's Army resigned Tuesday after 20 top military officials were fired.
More than 10,000 rebels continue to fight and some paramilitary groups have rearmed.
Demonstrators from presidents to pop stars filled the streets across Colombia and in 80 cities worldwide, demanding that FARC release all remaining hostages.
After a series of setbacks, leftist President Hugo Chávez welcomed his conservative nemesis – Colombia's Álvaro Uribe – to a reconcilatory meeting on Friday.