system
Given the following post, respond as if you're commenting on Reddit:
human
Why does America(among others) have different laws for different states and other countries just have the same laws throughout the country.
gpt
Federalism! 

American federalism emerged from the particular way in which the states declared independence from Britain-becoming, in effect, separate countries-and then joined together to form a confederation and then a single nation.  Recall that the framers of the Constitution turned to federalism as a middle-ground solution between a confederation form of government-which was deemed a failed model based on the experience of the United States under the Articles of Confederation-and a unitary form of government-which a majority of states, jealous of their independence and prerogatives, found unacceptable. Federalism was also a form of government that was consistent with the eighteenth-century republicanism of the framers because it helps fragment government power. But we can gain further insight into why the United States adopted and has continued as a federal system if we look at what other countries with similar systems have in common.

Federalism tends to be found in nations that are large in a territorial sense and where the various geographical regions are fairly distinctive from one another in terms of religion, ethnicity, language, and forms of economic activity. In Germany, for example, the conservative Catholics of the south have traditionally been different from the liberal Protestants of the north and east, while the former communist territories of the former Germany Democratic Republic differ markedly in living standards from the prosperous West. In Canada, the farmers of the central plains are not much like the fishers of Nova Scotia, and the French-speaking (and primarily Catholic) residents of Quebec differ markedly from the mostly English-speaking Protestants of the rest of the country. In Spain, deep divisions along ethnic and language lines (note the distinctive Basque and Catalan regions). Other important federal systems include such large and richly diverse countries as India, Pakistan, Russia, and Brazil. In these countries, federalism gives diverse and geographically concentrated groups the degree of local autonomy they seem to want, with no need to submit in all matters to a unified central government. In Iraq, the question of the relative degree of autonomy of Kurdish and Shiite provinces in a federal Iraq was the most important point of contention over adoption of a new Iraqi constitution in 2005.
The United States, too, is large and diverse. From the early days of the Republic, the slave-holding and agriculture-oriented South was quite distinct from the merchant Northeast, and some important differences persist today. Illinois is not Louisiana; the farmers of Iowa differ from defense and electronics workers in California. States today also vary from one another in their approaches to public policy, their racial and ethnic composition, and their political cultures.  In The Federalist Papers, the Founders argued that this size and diversity made federalism especially appropriate for the new United States.

While the American system of federalism was truly exceptional at the founding, other large and important countries have taken on federal forms in the years since, especially since the end of World War II. To this extent, the United States is no longer the single exception or one among a handful of exceptions to the unitary nature of the majority of the world's governments.