A state, simply speaking, is a political entity, with certain features, like a government with at least some sovereignty and borders. As opposed to a nation, which can be considered a people with a common identity and usually a common language, that may or may not share religious or other cultural institutions, and may or may not be included in the same politically designated entity.

Germany, Spain, the UK and the rest are all states. You might contend that they are not states in the sense of the United States, but only because you don't get that the USA were established as independant entities first, and that the United States of America is to New York and New Jersey as the EU is to France or Italy. The subsequent erosion of the independent character of the American states, increasing encroachment of Federal power over state prerogatives, and their common language and general cultural homogenity might deceive people into believing that they are more like provinces than sovereign entities but whatever the de facto relationship of the states to one another and the union, they are de jure independant political entities.

And that same issue of increased membership also applies to the reparations question. Nevada joined the USA during the Civil War, which eradicated slavery, and West Virginia broke off from Virginia after the latter seceded, but prior to the outbreak of fighting. Those two states specifically joined the country on the side that was fighting to END slavery. Fourteen other states have joined the USA since the war ended and slavery was abolished, and 23 other states raised from among their citizenry, regiments of soldiers who shed blood on the side that opposed slavery. That, BTW, is one more indication of the discrete political character of that states, in that it was largely the states who raised and equipped volunteer units that provided the bulk of the Union forces in the War Between the States. The question of to what degree Bulgaria or Croatia should be taxed so the EU can repay Africa for the colonization, is not at all disimilar to the question of how much the citizens of Idaho and Wyoming and Hawaii owe for the institution of slavery, which was abolished a generation (almost a century in the case of Hawaii) before they entered the United States.