Yes, if practiced as intended, which there is no guarantee.

Did Italy do that?

Perhaps not as quickly as they should have. The rest of the world is learning from Italy's experience (they should have been paying closer attention to China, but that's another story)

Another thing to realize is that these numbers you are seeing are WITH CONTROLS. Sure, "only" 3,000 Chinese have died. Maybe it's more than that, it's hard to trust Chinese numbers. But even at 2x or 3x, that's far cry from the millions it could have been, had China not both imposed extreme controls to limit the spread of the disease AND allocated emergency resources to healthcare.

Some models show realistic scenarios where 5 million Americans die within a year, if the virus is allowed to spread at its maximum rate.

That would imply 100% infection, at a base reproduction rate of 15 (close to measles), and a mortality rate of 30% (close to Ebola).

If left unchecked covid-19 would infect 100-250 millions Americans. The R0 is 2.5-3. The average mortality rate is said to probably be closer to 1% rather the 3.4% previously advanced, so 1-2.5 millions deaths, which we will hopefully never reach if people follow the current social distancing and self-quarantine guidance.

That would implies 100% infection, at a base reproduction rate 15 (close to measles), and a mortality of 30% (close to Ebola).

If left unchecked covid-19 would infect 100-250 millions Americans. The R0 is 2.5-3. The average mortality rate is said to probably be closer to 1% rather the 3.4% previously advanced, so 1-2.5 millions deaths, which we will hopefully never reach if people follow the current social distancing and self-quarantine guidance.

Italy should not be looked to as a model of how to handle this.