Formal and Informal 2nd Person

Why do so many western Eupopean languages have both formal and
informal forms of the 2nd person and am I correct in believing that
they are relatively recent phenomena; from the last five or six
hundred years perhaps? Did they develop as a result of social change
for instance the rise of a landlord class? I sure that Latin did not
distinguish between formal and informal address. Also are formal and
informal forms found in Slavic, Indic languages as well? Enough
questions for now I look forward to your replies.
David James