Why did Britain change its strategy to focus on the Southern colonies in the summer of 1778?

The French allied with the colonials, and the British believe they had supporters in the south.

Explanation:

The French signed a treaty with the colonials in 1778 which forced the British to rethink their tactics.  They were now having to fight both the newly formed Americans and the French.  The British falsely believed they had more colonial supporters in the south, so began to focus their efforts there in attempt to subvert the French involvement.  This lead to the colonials fighting the British in the south with guerrilla warfare tactics instead of proper field combat, as the British were use to.  For America, the French helped a ton when they joined the war (Thanks Benjamin Franklin).

a politically correct answer.

northernmost part (disputed, administered) - near indira col, siachen glacier - 35.674520°n 76.845245°e

northernmost part (disputed, claimed) - dafdar near beyik pass - 37°24′00″n 75°24′00″e

northernmost part (undisputed) - near dharwas, chambal district - 33.24902°n 76.82704°e

southernmost part (mainland) - cape comorin - 8.06890°n 77.55230°e

southernmost part - indira point in the nicobar islands - 6.74678°n 93.84260°e

distance between:  

1 & 4 - 3070 km

1 & 5 - 3654 km

2 & 4 - 3269 km

2 & 5 - 3885 km

3 & 4 - 2801 km

3 & 5 - 3430 km

explanation: