Why did the large numbers of loyalists moved to cities in the south in the years 1779 and 1780? and why they left those cities when they did?

The Continental victory at Saratoga in 1777 and the Treaty with the French in 1778 transformed the war, especially for the British. Increased French aid to the Continentals was very slow in coming; coordinated military activity between the two new allies was even slower to happen. Meanwhile, the British were immediately faced with a global conflict with France. As a result, the British changed their strategy yet again in 1778. Rather than mounting a full-scale military campaign against the Continental Army, the British decided to focus their efforts on the loyalists, who they still believed were the majority of the American population.

Believing the loyalists were strongest in the South and hoping to enlist the slaves in their cause--an objective that seems incompatible with a focus on Southern loyalists--the British turned their efforts to the South. In fact, the British had some important military successes in the South. They occupied Savannah, Georgia, in late 1778 and Charleston, South Carolina, in May 1779. They also struck a disastrous blow on General Horatio Gates' forces at Camden, South Carolina, in August 1780.

Although the British were successful in most conventional battles, the fighting in the South, under the leadership of Generals Nathanael Greene and Daniel Morgan, turned toward guerrilla and hit-and-run warfare. Moreover, the British had overestimated loyalist sentiment in the South; their presence actually forced many, who had been sitting out the war, to take sides, most in favor of the Patriots. At the same time, the British underestimated the logistical problems they would encounter, especially when their army was in the interior away from the supplies offered by their fleet. Patriot forces, on the other hand, were supplied and could hide among the local population. As a result, the British southern strategy was a dismal failure.

c.) biotic: snails; abiotic: temperature climate