To refuse to help (someone in trouble or need.)
Отказать кому-либо в помощи, когда этот человек в нужде или трудной ситуации.
He turned his back on his own family when they needed help.
She turned her back on Hollywood and went to live in Florida.
Она отказалась от Голливуда и отправилась жить во Флориду.
The poorer nations are often not grateful for our help, but still we can not turn our back on them.