It'll make more sense if you compare the United States to the European Union, with each American State being it's own country.

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Both are:

• made up of individual member states that have their own distinct cultures and values
• are a political and economic union of member states
• promote use of a single currency
• allow for free movement of people, goods, and labor between each member state
• are subject to supremacy laws, in which the union's laws take priority over the individual member state's laws. Think Federal vs State law in US, or EU law vs Germany.

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Viewing the US as a Union rather than a homogeneous country will make more sense as to why states vary so wildly from each other. Instead of California vs Texas, think Sweden vs Poland.