Spanish is one of the easiest languages for English speakers to learn, even if they have never learned another language. English and Spanish share the same alphabet, along with several hundred cognates, which are words derived from the same root and have similar meanings spellings and even pronunciation.
A person's native language strongly influences which languages they can learn easily. Someone who speaks a European language potentially has a harder time learning an African or Asian language than they have learning a different European language. The similarities of alphabet, vocabulary, grammar and cultural assumptions within language groups seem to bind together those who speak the languages, making the learning process more successful.