Spanish is easy to learn because its spelling is phonetic (it reads the same as it sounds). So when you read a word in Spanish, you know exactly what it will sound like when spoken, a tremendous advantage for students.
Spanish is a language rich in History. It was born from the ruins of Latin, the language of the Roman Empire who arrived to Hispania in the year 218 B.C., moving away the local languages of the Iberian and Celt tribes. As a Romance language like French, Italian or Portuguese, in many ways it is a dialect of Latin, so for Westerners at least, much of the vocabulary is familiar.
After the weakening, fragmentation and fall of the Roman Empire of the West, Latin language followed its own way, in which the traditional forms of expression and the new linguistic habits developed by these speakers thanks to the migratory flows came together. From IXth to XIIth century, new forms of expression called "romances" emerged followed later by the peninsular Romance languages like Leonese, Castilian, Galaic-Portuguese or Catalan, independent from Latin, and each one with its own system.
But was Spanish Castilian the language destined to be one of the most spoken anywhere in the world due the Castilian expansion, first through the Iberian Peninsula and then in the Americas colonization.