Why has tax policy long ago left a dependency on tariffs and shifted to a dependency on the income tax?

Consider tax policy that encourages home ownership of a primary residence in the US and that of rental property as well.
Why does the government encourage this?
In what ways, via tax deductions and tax credits, does the government encourage home ownership?
What is the basic tax policy that causes the US to have a federal estate tax? Also, what is the difference between a gift tax (who pays it when it is due) and an inheritance tax (who pays it when it is due)?
How does the government manipulate its own spending/transfer payments and our tax rates to further its fiscal policy? What happens to each of these variables when the government is using an expansionary policy? what happens to each of these variables when the government is using a contractionary policy?
Why has tax policy long ago left a dependency on tariffs and shifted to a dependency on the income tax?