2. The U.S. - Canada lumber battle
The dispute had its origins in the 1980s, when American lumber companies said their Canadian counterparts weren't playing fair. Canada subsidizes lumber companies because the government owns many of the lands where the wood comes from. That subsidy -- on top of Canada's huge lumber supply -- allows Canada to price its lumber below what U.S. companies can charge.
The WTO ultimately denied America's claim and the two sides came to an agreement in 2006 to end the tariff so long as prices stayed within a certain bracket.