Tony Blair has used a keynote speech in South Africa to say there is a "moral obligation" to use political action "to make the world better".
Mr Blair, who promised more training for African peacekeeping forces and continued aid to the region, defended his interventionist foreign policy.
That policy, criticised after the Iraq war, had not managed to transform Africa but had made it better, he said.
Mr Blair is on his last big trip before stepping down as prime minister.
Mr Blair will hold talks with South African President Thabo Mbeki on Friday, when Zimbabwe's political crisis will be on the agenda.
He met South Africa's former leader Nelson Mandela on Thursday, who thanked him "for his support over the years" and said he looked forward to welcoming him to "the club of retiring presidents and prime ministers".
In his main speech of the tour, Mr Blair, who has sent UK troops into action in Kosovo, Sierra Leone, Afghanistan and Iraq while prime minister, said it was in countries' self interest to intervene in failing states.
He said: "I believe in the power of political action to make the world better and the moral obligation to use it.
"I do not believe that in this time - the early 21st century - that international politics can be just about nations' interests, narrowly and traditionally defined."
He said globalisation meant everyone had a stake in advancing "freedom, opportunity and justice for all".
And he: "Africa is close to my heart... it has also been at the top of my foreign policy for the last 10 years."
The Liberal Democrats described his speech as "trying to rewrite" his foreign policy legacy.
Foreign affairs spokesman Michael Moore said the "high points" of Kosovo and Sierra Leone had been "completely overshadowed by the prime minister's disastrous misjudgement over Iraq".
And Professor Ian Taylor, an expert in international relations, told BBC Radio 4's World at One programme said Britain needed a stronger political engagement with African leaders and to ask "tricky questions" about governance.
"It's not good enough simply to increase aid," he said.
Mr Blair has called on the G8 group of industrialised nations, meeting in Germany from 6-8 June, to be "bolder on Africa" and take a more strategic approach "based on partnership rather than aid alone".
"My belief is that we have to stay with it for the long-haul, commit and re-commit. Never let it be said that we are not trying even if it cannot always be said that we are succeeding."
He also said Africa should have a greater representation at international institutions, such as permanent representation on the UN Security Council.
Mr Blair was made an honorary paramount chief in Sierra Leone
On Wednesday, the prime minister held talks with President Ahmad Tejan Kabbah of Sierra Leone and Liberia's President Ellen Johnson Sirleaf.
And on Tuesday Mr Blair held talks with Libyan leader Muammar Gaddafi, saying relations between the UK and Libya had been "completely transformed" in recent years.
He has denied the week-long trip is a "vanity tour" - dismissing his critics as "cynical".
But on BBC One's Question Time, he was criticised by Tory frontbencher Caroline Spelman, who said the trip was "an indulgence" and asked why he had not visited Sudan's capital Khartoum to challenge the government on Darfur.
There was some criticism by panellists and members of the audience that the trip was aimed at reinforcing "brand Blair".
For the Lib Dems, Sarah Teather said there was a point to the trip, if Mr Blair raised the issue of Zimbabwe with President Mbeki and asked the African Union leaders for more action on Darfur.
But former Labour deputy leader Lord Hattersley added: "He shouldn't have done it."