Complex sentence: During the reign of her cousin, Anna (1730--1740), Elizabeth was gathering support in the background; but after the death of Empress Anna, the regency of Anna Leopoldovna for the infant Ivan VI was marked by high taxes and economic problems.
Split into simpler sentences: During the reign of her cousin, Anna (1730--1740), Elizabeth was gathering support in the background. After the death of Empress Anna, the regency of Anna Leopoldovna for the infant Ivan VI was marked by high taxes and economic problems.