Some of the reasons the war produced such changes are easy to see, because they were immediate at the time. The National League of Women's Service brought women together to serve the country and support their men. This means women got lots of experience raising money, organizing public events, doing public speaking, etc. This provided a frame for later action. With so many men gone, a number of women worked outside the home for the first time, exposing them to greater ranges of experiences and new people. Men returned from the war injured; some did not return at all. This left a gap that women filled.
Other social changes happened near that time, but not for that particular reason. For example, Margaret Sanger opened the first birth control clinic in the United States in 1916. The social changes that flowed from this weren't caused by the wars, but overlapped with it. Likewise, the suffrage movement was well underway, but was given power by women's support of and resistance to the war.
Prior to WWI, woman's role was to handle domestic affairs at home, to take care of the family. Some of the fortunate ones got to work in the textile manufacturing industries or as teachers in schools.
But, during the course of WWI, many men were enlisted into the army as soldiers to fight Germany assault, so there was a shortage of manpower and labor in different sectors of the economy, so women came into the helm to take over the jobs previously taken by Man. They work in the ammunition factory, offices and large aircraft hangars, which Man previously didn't believed that woman can work at that type of jobs, but by this experience, they have a different perspective towards woman, so showing the equality of the opposite sexes, that woman can do jobs that man can do. Woman were also enlisted into the Army in the form of nursing to take care of the soldiers' welfare.