The refusal of many states to recognize expatriation became problematic for the United States, which had a large immigrant population. The War of 1812 was caused partly by Britain's impressment of US citizens born in the UK into the Royal Navy. Immigrants to the US were sometimes held to the obligations of their foreign citizenship when they visited their home countries. In response, the US government passed the Expatriation Act of 1868 and concluded various treaties, the Bancroft Treaties, recognizing the right to renounce one's citizenship.