Trade is related to Economics. Economics is related to Depression. Depression is related to Valley. Valley is related to Surrounding. 
you are likely to find War in/at/on City. City is the opposite of Forest. 
Trade <--RelatedTo--> Economics <--RelatedTo--> Depression <--RelatedTo--> Valley <--RelatedTo--> Surrounding 
War --AtLocation--> City <--Antonym--> Forest 