The federal government expanded the national parks system due to the financial benefit of setting aside land assets to borrow against.
the need to use federal land for the expansion of the transcontinental rail system.
the activism of environmental groups like the Sierra Club and the National Audubon Society.
the lobbying of urban progressive groups to preserve endangered wildlife on protected land.

2/B - the need to use federal land for the expansion of the transcontinental rail system.

Explanation:

The 1966 Act required that all historical parks be entered in the National Register of Historic Places. Along with the Wild and Scenic Rivers Act, this legislation expanded the diversity of units in the National Park System.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).

it increase by 12% a year from 1812-1820