Neoclassicism was active during the mid-18th century to the end of the 19th century (1750s-1890s). Archeological discoveries that were being made in Greece and Rome at the time invoked revived interest in the study of classic art and literature, thus bringing about Neoclassicism.
The Neocalssical movement was caused by a desire for the stability of the Middle Ages. Romanticism actually sprang from the Napoleonic Era. Neo classicism came first.