The Conservative movement was originally a 19th century reaction to Reform, from within the Reform community. They returned to accepting both Torah and Halacha as authoritative. But because this was a distinct community, their application of Halacha to contemporary situations took an independent course from the orthodox application of Halacha. Nevertheless, differences in prescribed behavior are actually quite small. The waves of Jewish immigration to America from the 1880s to the 1920s resulted mostly in enlarging orthodox and conservative congregations.
Most American Jews identify themselves as Conservative. But most of these Jews are not observant of Conservative halacha and are unfamiliar with it. This is the most significant practical distinction between Orthodox and Conservative. Thus, most American Conservative Jews practice Reform Judaism in deed and philosophy, but join Conservative synagogues because that is the style of service they prefer. Their affiliation has become a matter of community more than a matter of philosophy or of forms of observance.