Which constitutional principle describes the division of powers between the federal and state governments?

The answer is  Federalism.

Explanation:

Federalism is the sharing of power between the different layers of institutions or organizations. It means that both have exclusive power and are in a negotiable relationship. In federalism, there are both national and state-level elections and power is divided between them based on functions of national concern and state-controlled program.

answer: the time zones used to be whatever the local authority wanted them to be. one town might have 6am whenever the sun came up and another town had 6am 10 minutes later.  

the trains had a hard time when their orders said to be at a certain point at 6am.  

6am, but who's 6am.  

the railroads got together and set the time zones more or less along the longitude lines across the country.

explanation:

immigrants from northern and western europe continued coming as they had for three centuries, but in decreasing numbers