No, they were not organized in spontaneous protest to Trump. They were organized to kick off Hillary Clinton's agenda as president, and intended to celebrate her inauguration. But then she did the unthinkable and lost. The left didn't want to waste so much of George Soros's money, so they repurposed the march.
I think the march was a mistake. As a celebration of Hillary's election, it could have worked. As a protest against Trump... well, women in modern industrial societies are simply not oppressed. Equal rights, equal pay for equal work, access to health care, no need to wear a "modesty garment" or be subject to the whims of your male relatives, the list goes on and on. Give women what they want, it seems, and they'll wear pussy hats and scream at you anyway.