Complex sentence: About 3,000 French joined with 2,000 Americans in the Siege of Savannah, in which a naval bombardment was unsuccessful and then an attempted assault of the entrenched British position was repulsed with heavy losses.
Split into simpler sentences: About 3,000 French joined with 2,000 Americans in the Siege of Savannah, in which a naval bombardment was unsuccessful. An attempted assault of the entrenched British position was repulsed with heavy losses.