The fourth era of american political party history, which began in 1968, is characterized by

A divided government.

Explanation:

A Divided Government is when a party controls the executive branch when the other party controls one of both houses of the legislative branch. When Richard Nixon was elected in 1968 the government became divided. Since then, Republican presidents needed to deal with a Congress that as mostly controlled by the Democrats.

mount st. helens in washington erupts, causing a massive avalanche and killing 57 people on this day in 1980. ash from the volcanic eruption fell as far away as minnesota. seismic activity at mount st. helens, which is 96 miles south of seattle, began on march 16.