Leftist leader Gustavo Petro was sworn in Sunday as Colombia’s new president with the challenge of delivering on promises to achieve social equality, fighting climate change, achieving peace in the country and ending a "failed" war on drugs.

Along with his running mate Francia Marquez, who became the first Black female vice president in the nation's history, Petro took over the presidency from his predecessor, right-wing President Ivan Duque, who failed to tackle unemployment, rising poverty, and violence against human rights leaders during his term.

Petro, a former member of the leftist M-19 guerrilla movement and Bogota mayor, won Colombia's presidential election by a narrow margin, promising to address widespread poverty and inequality.

In his first speech as president, Petro said that “10% of the Colombian population has 70% of the wealth. It is nonsense and an amorality. Let us not naturalize inequality and poverty,” as he was surrounded by delegations from foreign governments and various heads of state.

Among the guests who attended the event were the King of Spain, Felipe VI, Argentina’s President Alberto Fernandez, Chile’s President Gabriel Boric, Ecuador’s President Guillermo Lasso and a top-level delegation from the US government. Peru’s President Pedro Castillo was invited but could not attend after lawmakers rejected his request to travel to Bogota as he is facing five investigations for alleged corruption.

Petro’s arrival to the presidency has generated optimism among Colombians who believe in many promises made by the newly elected president.

He has vowed to halt oil development even though the oil industry makes up the country's biggest exports and has also promised to implement a 2016 peace deal with the Revolutionary Armed Forces of Colombia (FARC) and seek peace talks with rebels from the National Liberation Army (ELN) who continue to commit crimes and kill police officers.

“This is the government of life, of peace, and that is how it will be remembered,” Petro said.

In his speech, Petro spoke about ending the “failed war on drugs" and moving to a "policy of strong prevention of consumption" in developed countries, challenging the "decades" of anti-drug persecution that Washington has encouraged.

"It is time for a new international convention that accepts that the war on drugs has failed," he said.

Petro’s arrival to power also means that Colombia and Venezuela will reestablish relations after years of tensions. The foreign ministers of both countries announced that as of Aug. 7, when the newly elected president takes office, ambassadors will be appointed and consulates will reopen.

Some 100,000 Colombians also attended venues where there were more than 1,000 artists in various parts of the country to mark the day.

After being sworn in, the president walked to the Casa de Nariño, the presidential palace, which looks out upon the central Plaza de Bolivar in Bogota.