The fight over healthcare is leading some to consider something radical

Since Republicans took over Congress, Obamacare has become more popular. Surveys from the Kaiser Family Foundation show the number of Americans supporting it went from 38% a year ago to 49% today.

But Obamacare, itself a compromise, has real problems, and its limitations - and the growing backlash to Republican efforts to repeal it - have given an opening to an idea that until now has had little traction in the US.

The idea is single-payer healthcare, and if the US adopted it, it'd be a radical change. At its core, the idea is that the government, in some form, would pay for all or most healthcare expenses.

In business circles, states, and even the top levels of some insurers bringing some form of a single-payer healthcare system is beginning to gain traction.

California's legislature is considering a bill that would institute a single-payer system, and Nevada's legislature just passed a bill to expand publicly funded Medicaid to all residents.

Business leaders including famed investor Warren Buffett and Charlie Munger said that single-payer healthcare is the solution to the increasingly high levels of healthcare expenditures in the US. Even Aetna CEO Mark Bertolini, the top executive at one of the five major publicly traded US insurers, said at a staff meeting in May that a modified form of single-payer is a "conversation" the US should begin to start.

On Capitol Hill, while the American Health Care Act would take the US further away from single-payer, Sen. Bernie Sanders has again introduced his Medicare-for-all bill that would create a single-payer system.

During his campaign, Sanders showed that the appetite among the American left is growing for the policy. So what exactly is single-payer?

While it may seem simple enough, there are actually a number of different forms a government-funded healthcare system could take.

We've broken down the single-payer healthcare systems in Canada, the UK, and Taiwan, along with one non-single-payer but intriguing option in Germany, to see where the US system could go next. While these breakdowns aren't comprehensive, they highlight the types of single-payer systems that the world uses.