> Each of their component countries have their own president, their own political countries, and in a good part and their own policies, besides the group common policies.

US states have their own governor, their own political counties, and in a good part and their own policies, besides the common group policies.

> Would you put California, Wall Street, Shenzhen and a few more at the same level as countries?

Tennessee has approximately the same population, GDP, land area, etc. as Ireland. Texas was an independent country before it was a state.