Final answer:
The African American Civil Rights movement and the feminist movement were highly impactful social movements, radically challenging the status quo of 1960s-70s America through direct action and strong advocacy for equal rights.
Step-by-step explanation:
Among the social movements of the 1960s-70s, the African American Civil Rights movement particularly challenged mainstream America. By seeking to dismantle systemic racism and achieve equal rights through legal changes and social action, it gained national attention and drove legislative changes.
What made some aspects of the movement seem radical were the methods of direct action, such as sit-ins, freedom rides, and marches, often met with violent opposition, and the assertive rhetoric of groups like the Black Panther Party. The feminist movement of the same era also arguably challenged the status quo, with activists advocating for reproductive rights, workplace equality, and challenging traditional gender roles. These movements were considered radical for their direct challenges to established societal norms and for their demands for immediate and substantial changes to the social and political order.