This article is from the Ballet and Modern Dance FAQ, by Tom Parsons firstname.lastname@example.org with numerous contributions by others.
Modern dance has its roots in the late 19th century, but is mainly
a 20th-century phenomenon. To some extent, it was a reaction against bal-
let. (Isadora Duncan, one of the best-known pioneers, claimed that ballet
"deformed" the body.) When you consider the condition of ballet in most
of Western Europe at the time, this is not surprising. One might say that
it was as much a response to this as Diaghilev's company was. Diaghilev
responded by importing dancers and fresh ideas from Russia; the moderns
responded, initially, by rejecting the traditions of ballet altogether as
sterile and irrelevant to the new century. They were searching for
naturalism and, above all, expression.
But the reaction against ballet must not be exaggerated; new
movements in the arts frequently start with a rejection of what has gone
before. In a larger sense, modern dance was also part of the general trend
toward modernism in all the arts that has marked this century, and this is
probably a more important cause than any rejection of ballet. In addition,
there has been a fair amount of cross-fertilization between ballet and
modern, and althought they may well continue to be separate traditions, the
gulf between them has narrowed over the century.