As Europe began crumbling in 1939, a new generation was jolted.

That's true of the fictional characters at the core of World on Fire, the sweeping mini-series that starts Sunday on PBS at 9 p.m. ET (check local listings).

"They were all kids…going through the kinds of things that we go through now – friendship and heartbreak and falling in love and making these terrible mistakes," Jonah Hauer-King, who stars as translator Harry Chase, told the Television Critics Association in January. "But the stakes were so high."

And it's true of the real-life people at the time. Peter Bowker, who created the series, recalls reading the diaries of two young women: One "said, 'today I joined the Resistance.' And then there would be four paragraphs that would be about boys and finding good coffee."

So he created two extraordinary women: Kasia (like one of the diary-writers) is a waitress; Lois is a factory worker who (like Bowker's grandmother) sang to the troops.

Kasia is Polish, Lois is English, both are working-class women with steely resolve. And thrown between them is Harry – rich, educated, a good guy who's ill-prepared for hard times.

The story has a few older characters on the edges, with well-known actors:

Sean Bean – often a warrior in projects such as Game of Thrones and Lord of the Rings – gives a moving performance as Lois' father, a peace activist who was shell-shocked in World War I.

Lesley Manville, an Oscar-nominee for Phantom Thread, plays Harry's mother, devoid of maternal instincts, and short on human instincts.

And Helen Hunt, an Oscar-winner and four-time Emmy-winner, plays an American radio reporter in Germany. In the first moments, she sees an atrocity that, Hunt says, was based on real life: "What you see are German soldiers shooting Germans and putting them in Polish uniforms so the Nazi regime can say, 'They were coming after us. (It's) a fake victimhood, 'therefore, I can attack.'"

Sweeping across Europe, the story also follows Kasia's brother, Lois' brother, and the reporter's nephew, a doctor in Paris. But it focuses on the three young stars, who have some links to the story.

Zofia Wichlacz, who plays Kasia (top), is from Poland and has researched pre-war Warsaw. "We can see happy young people falling in love," she said, "in a city that's so vivid and so full of life."

Hauer-King's maternal grandparents fled from France before the Germans arrived. Playing Harry, a translator, he arrived with some knowledge of French then leaned on Wichlacz for the Polish.

And, Julia Brown, who plays Lois? Her grandmother (like Bowker's) sang to the troops. "My grandmother was actually a jazz singer in the war," Brown said. "She used to sing these songs to me when I was younger."

These are young actors – Wichlacz turns 25 on the day the show debuts in the U.S. – who are off to promising starts.

Brown, who's also a model and singer, has been a regular on British TV. Wichlacz was an unknown when she landed a lead role in Warsaw '44 (2014), winning the Polish version of an Oscar.

And Hauer-King? He was Laurie in the PBS version of Little Women and will be Prince Eric in the upcoming non-cartoon version of The Little Mermaid.

All will be back for the second World on Fire season – barring an overload of good fortune. "This young cast (will) be in demand," Bowker said. "And I'm thinking Little Mermaid 2 and Little Mermaid 3 will probably be taking Jonah's next five years."

The opener of World on Fire on Sunday is followed at 10 p.m. ET by The Windermere Children, a movie about a post-war program for young concentration-camp survivors (check local listings).