"New Zealand is a country heavily dependent on trade, particularly in agricultural products, as almost 20% of the country's
output is exported (by comparison it is 21% for the United Kingdom, 49% for Finland and 83% for Belgium). This leaves New Zealand particularly vulnerable to slumps in commodity prices and global
economic slowdowns. Its principal export industries are agriculture, horticulture, fishing and forestry making up about half of the country's exports. Its major export partners are Australia 22.4%, US 11.3%, Japan 11.2%, China 9.7%, Germany 5.2% (2004). " Source:
http://en.wikipedia.org/wiki/New_zealand#Economy
This shows it is dependant on not only the world economy (of which America is a HUGE part), but also on the US itself, being that it is its 2nd largest trading partner.
This is most likely not the only aspect, but since I cant find a good, spelled out source on the effect of the US on New Zealand other than this, we will leave it at that.
Note: I am from the US, just had some time, and got here before monty.