Complex sentence: By 1433, the Duke of Burgundy had assumed control over most of the lowlands territories in Lower Lotharingia; he created the Burgundian Netherlands which included modern Belgium, Luxembourg, and a part of France.
Split into simpler sentences: By 1433, the Duke of Burgundy had assumed control over most of the lowlands territories in Lower Lotharingia, creating the Burgundian Netherlands. This also included modern Belgium, Luxembourg, and a part of France.