1.   Sino-U.S. relations have also been troubled by disputes over human rights, trade and arms control.

2.   U.S.-Mexican relations have been troubled by disputes such as drug trafficking, corruption and abuse of migrants trying to cross the border into the United States.

3.   But preparations have in some cases been troubled by disputes over protocol and historical interpretation.

4.   The new secretary-general said he wanted to improve cooperation between NATO and the United Nations which has been troubled by disputes over policy in the conflict in former Yugoslavia.