Later it was restricted or forbidden by most world religions, but it was not considered an offense in secular law until the 19th century. During that century, first the English Parliament and then American state legislatures prohibited induced abortion to protect women from surgical procedures that were at the time unsafe, commonly stipulating a threat to the woman's life as the sole (“therapeutic”) exception to the prohibition. Occasionally the exception was enlarged to include danger to the mother's health as well.
Legislative action in the 20th century has been aimed at permitting the termination of unwanted pregnancies for medical, social, or private reasons. Abortions at the woman's request were first allowed in post-revolutionary Russia in 1920, followed by Japan and several East European nations after World War II (1939-1945). In the late 1960s liberalized abortion regulations became widespread. The impetus for the change was threefold: (1) infanticide and the high maternal death rate associated with illegal abortions, (2) a rapidly expanding world population, (3) the growing feminist movement. By 1980, countries where abortions were permitted only to save a woman's life contained about 20 percent of the world's population. Countries with moderately restrictive laws—abortions permitted to protect a woman's health, to end pregnancies resulting from rape or incest, to avoid genetic or congenital defects, or in response to social problems such as unmarried status or inadequate income—contained some 40 percent of the world's population. Abortions at the woman's request, usually with limits based on physical conditions such as duration of pregnancy, were allowed in countries with nearly 40 percent of the world's population.

U.S. Legislation
In the United States, legislation followed the world trend. The moderately restrictive type of abortion law was adopted by 14 states between 1967 and 1972. Alaska, Hawaii, New York, and Washington legislated abortion on request with few restrictions. In 1973 the Supreme Court of the United States, in the case of Roe v. Wade, declared unconstitutional all but the least restrictive state statutes. Noting that induced early abortions had become safer than childbirth and holding that the word person in the Constitution of the United States “does not include the unborn,” the Court defined, within each of the three stages of pregnancy, the reciprocal limits of state power and individual freedom:
“(a) During the first trimester, the abortion decision and its effectuation must be left to the medical judgment of the pregnant woman's attending physician.