Early in their career, Europe was their biggest market. But after they debuted their American album in 1997, the US became their main market. Majority of their concerts were/are in North America. However, their international fans seemed more passionate though.
A breakdown of their last world tour (shows):
North America: 82
South America: 10
Australia/New Zealand: 5
Middle East: 3
They had the most success globally in the 90s/early 2000s followed by Westlife (popular everywhere except the USA). N'Sync was big in America, but wasn't as popular internationally. Not sure if BSB still holds the 1st week international sale record, but their Black&Blue album sold 5 million copies. Shortly afterwards, they went into hiatus and their fanbase took a dive. N'Sync holds the American 1st week sale record at 2+ million copies.
Their popularity is not what it was, far from their $300+ millions grossed tour in 2001 (though they never did finish that tour because of 911 attack) but they are doing pretty decent for a bunch of guys in their 30s/40s. Their fans are not teenagers anymore so I don't think they are really into these types of stuff (voting)...majority of them are moms and are busy.