why did many women replace men as factory workers during world war 2? in the book, A People of the United States, by Howard Zinn, he quotes "a...

First one must consider the source. Howard Zinn during his
lifetime was an outspoken socialist who offers alternative views of American history.
Since his views are not mainstream, one must accept them in the way that Zinn
intended.

By militancy and crusading spirit, Zinn indicates
that the entire country was caught up in the war, as it had been in World War I. Both
World Wars were the first in history in which total mobilization was employed,
especially WW II in the U.S. when new automobiles and appliances were not produced, and
pennies were made of steel to support the war effort. Women worked in factories to
replace the men who were fighting the war; however even this was couched in terms of
women doing their part to win the war. The famous image of "Rosie the Riveter" depicts
her as contributing to the war effort in her own special way. To Zinn, this was a
classic "us vs. them" controversy in which the U.S. considered itself right and engaged
in a righteous crusade against an unholy enemy. The term "crusade" has often been used
in U.S. initiatives, whether military or otherwise; but the term has fallen out of favor
recently due to Osama bin Laden's references to "crusader America," an obvious reference
to the abuses of the crusades of the Middle Ages.

The
obvious connotation of Zinn's remarks is pejorative; but this is exactly what he
intended. He should be read not so much to learn the history as to analyze and interpret
the meaning of events.  So, Zinn's remark means that the people of the U.S. engaged in a
zealous and righteous campaign to fight the war.