America's central bank HAS dumped $ over the last 3 years. That was to stop what these other nations were doing. Had they not been manipulating, then when we dumped our $, and if they kept theirs at a set amount, then the foreign money to the $ would have dropped (i.e. more $ to the ruppe/won/yuen/etc). That was NOT the case. Instead, it continued rising relative to the $.
Now, as to other moneys, NZ's dollar dropped because the one-way trade with US increased, combined with US$ dumping $ to stop these other nations from trying to sink America. And our central bank has HELPED NZ with that.