when governments spend implement policies that keep taxes low subsidize the price of staple goods or use other methods that effectively put more money in people s pockets consumers have more money to spend as most economies rely at least partly on imports for many goods and services this increased spending creates demand for foreign currency usually u s dollars as importers have to sell local currency and buy foreign currency to pay for imports 
demand for foreign currency and selling of local currency to buy it increases exponentially when those policies also promote heavy investment in infrastructure new businesses and other economic projects as more local currency is offered for sale on foreign exchange markets its value goes down unless there is a corresponding demand to buy it say by exporters selling foreign currency that they earn from exports 