Video report by ITV News Royal Editor Chris Ship
Prince Harry said it had been "emotional" retracing the steps made by his mother, some 22 years after she walked through a minefield in Angola.
The Duke of Sussex, who is the visiting the country as part of his tour of Africa, paid tribute to Diana's legacy as he toured the now developed area.
He said: "To see the transformation that has taken place from an unsafe and desolate area into a vibrant community of local businesses and colleges.
"22 years ago, my mother visited Angola. There were still more than 1,000 minefields in this beautiful country which remained to be cleared
"I wonder if she were still alive today, whether that would still be the case. I'm pretty sure she would have seen it through," he added.
He took a moment to sit beneath a tree, planted in the town of Huambo, named after his late mother.
Harry opens up about the emotional trip to Angola, and his mother's legacy
ITV News Royal Editor Chris Ship said landmines are still a "very unfinished business" in the central African nation.
About £350 million is needed to clear Angola's 1,200 minefields by 2025, as set out in a treaty around the clearance of mines.
The Halo Trust, which works to clear landmines in Angola, hopes the visit of the duke will bring more attention to the country's clearance operations and direct money towards the work.
The charity says it has destroyed almost 100,000 landmines in Angola since 1994.
Earlier in the day, the duke donned body armour and a protective visor to explode a mine before making a speech, praising the clearing efforts by the Halo Trust as helping the community to "find peace".
He said: "Landmines are an unhealed scar of war. By clearing the landmines we can help this community find peace, and with peace comes opportunity.
"Additionally, we can protect the diverse and unique wildlife that relies on the beautiful Kuito river that I slept beside last night.
"That river and those wildlife are your natural assets and, if looked after, will bring you unlimited opportunities in the conservation-led economy."
- ITV News Royal Editor Chis Ship talks about Harry's visit to the former minefield
He went on to say: "Later today I will visit Huambo to see the place where my mother walked through a minefield in 1997. Once heavily mined, the second city of Angola is now safe.
"With the right international support, this land around us here can also be like Huambo. A land free, diverse and dynamic, a thriving community, connected to and benefiting from all that it has to offer."
Near the south-eastern town of Dirico, the duke walked into an area that was once an artillery base for anti-government forces who had mined the position in 2000 before retreating.
The dusty scrubland was marked with red warning signs showing the skull and crossbones, with the Portuguese words "Perigo Minas!" and the English translation below - danger mines.
Harry explodes landmine in Angola minefield
Jose Antonio, a regional manager for the landmine clearance charity the Halo Trust, took Harry onto the site where his staff have been working since August to make it safe, and he hopes they can complete their painstaking clearance by the end of October.
Like all those visiting the Trust's site, Harry had been given a safety briefing and told not stray of the cleared lanes, touch anything or run.
He watched as a mine clearance worker used a metal detector to search for the mostly anti-personnel mines buried in ground.
If one is discovered staff are trained to move back and carefully remove the soil as they move forward until they reach the munition.
The duke walked through an area of the site looking at the marked off areas which potentially could contain landmines.
An anti-personnel mine had been discovered earlier and Harry was asked to set it off with a controlled explosion to safely destroy the decades-old weapon.