This article looks at how trade and integration affect countries at different levels: national, regional, and global. The researchers used computer models to predict the outcomes of trade policy changes in three cases: Finland joining the EU, global trade agreements through the WTO, and the EU expanding to include former socialist countries. They used different models for each case, like a model of the Finnish economy for EU accession. The main findings show that trade policies and integration can have significant impacts on economies, and these models help predict what might happen in different scenarios.