Most important is the over-use of antibiotics in wealthy countries. Important, too, is patients not completing their treatment courses, stopping as soon as they get better. In poorer countries, some of the drugs prescribed to ill people are substandard, resulting in a lower dose than needed. This favors the development of resistance. Another important cause is the feeding of low levels of antibiotics to animals to promote growth.
Health is a trans-national issue.
Actions taken in one group of countries have direct impact on health risks elsewhere. And not just in neighboring nations. It could have led to a trade war. Two million people cross international borders every single day, about a tenth of humanity each year. And of these, more than a million people travel from developing to industrialized countries each week.