If something happens "in" Delaware, that might mean that it's only in one specific city or one part of the state. But something that happens "throughout" Delaware is all over the state, or in several different locations spread across the state.

Things can happen "throughout" a country, a state, a region, a company, an industry, a building, etc. You can also talk about things that happen "throughout" a time period:

England and France repeatedly warred with each other throughout the Middle Ages.