The 34-year old midfielder left Everton to join the Red Bulls in July 2012 and told NBC Sports that he would have had to pull the pin on his playing days for Australia if he happened to remain in the Premier League.
"If I stayed in Premier League, I would have to have retired from international football," he said.
"The demands of flying back and forth from England to Australia and wanting to do justice to my club side would be too much.
"I take the same approach now as I've taken in past years - it's just that in MLS the demand of games and travel time isn't as high as the Premier League.
"It hasn't been easy coming to MLS. Physically, it's demanding. Every player is exceptionally fit and it shows on the National Team."
Cahill added: "I need to play as many games as possible before going to the World Cup (in Brazil later this year). I want to do well for Red Bulls which means automatically I'll be ready to get on that plane for Australia come June."
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