What cause was the focus of Live Aid's fundraising efforts?

The answer is: Ethiopian famine relief

Ethiopian famine relief became the rallying cry for Live Aid after Bob Geldof watched a BBC report about mass starvation in Ethiopia that left him completely shaken. He immediately started calling every musician he knew, organizing what became Band Aid and recording "Do They Know It's Christmas?" in 1984.

The success of that single lit a fire under Geldof. He figured if one song could raise millions, a massive concert could raise tens of millions. He pulled together what he referred to as a "global jukebox" of the biggest acts of the time. The bonkers lineup included Queen, U2, David Bowie, Madonna, and Led Zeppelin's first performance since John Bonham's death for two synchronized shows at Wembley Stadium and JFK Stadium.

From Freddie Mercury having 72,000 people at Wembley Stadium eating out of his hand during "Radio Ga Ga" to Paul McCartney belting out "Let It Be" to a global audience without realizing his mic was dead for the first two minutes, this was rock and roll actually changing the world, even if just for one day.

The whole thing came together in just 10 weeks. Artists flew between continents to play both shows, Phil Collins famously taking the Concorde from London to Philadelphia. The broadcast reached 1.9 billion viewers across 150 countries, raising about $127 million (with some estimates even higher) for famine relief.