The Spanish spoken in Spain is not, in fact, identical to the Spanish spoken in south and Latin America.

The most serious difference is that vosotros, the plural second person, doesn't exist in the Americas. Neither the pronoun vosotros (essentially a grammatically correct "y'all") nor vosotros' verb form (-éis, etc) are used. Instead, ustedes is always used when addressing groups ("ustedes" is plural "usted". "usted" is the honorary form of "you", and is treated by verbs as third person.)

While constant use of ustedes probably causes some ambiguity where vosotros (and its dedicated verb form) wouldn't, it causes no real incompatibility between dialects, since all it does is make anyone speaking American Spanish to appear unnecessarily polite when addressing groups.

enter subtle prompt here for anyone who can give other differences to post.