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She said divisions wrought by the 19th-century war were ably demonstrated by the map of states voting Democrat or Republican in this week's election.
Values and beliefs varied hugely from state to state, which made national health reform difficult because it aimed to standardise certain entitlements.
"We are not one country, we are many little countries."
President Barack Obama's re-election ensured a crucial element of the reforms, a requirement on people to have health insurance, should go ahead in 2014.
The reforms have been implemented in stages since Mr Obama's healthcare law was enacted in 2010.
Had challenger Mitt Romney been elected, she did not believe he would have made good on a promise to repeal the law, but he could have granted states waivers from its provisions.
Even when fully implemented, the reforms would leave millions of people without health cover, because of exemptions in who had to buy cover.
The law faced a major challenge in the Supreme Court this year, which confirmed the federal Government's right to make people buy insurance. This is critical because if people were not required to buy insurance, companies could not be made to cover such things as pre-existing conditions.
Prof Rosenau said she was often asked by her students whether she had been afraid when she lived in Canada to visit the "socialist" doctors there.
The healthcare reforms were opposed by 40% to 70% of the US public, depending how questions were phrased. However, the overwhelming majority agreed with individual components, such as forcing insurance companies to spell out their plans in plain English without confusing small print.
"We do not have a sophisticated population," she said.
Even the people with the most to gain from reforms opposed them, displaying a tendency to put ideology before their self-interest, she said.
The insurance reform brought the industry into the 21st century, she said.
Prof Rosenau is visiting the University of Otago as a William Evans Fellow. Her talk was organised by the Dunedin School of Medicine's Centre for Health Systems.