The Second Indo-Pakistani War, also known as the 1965 War, was a military conflict between India and Pakistan that occurred from August to September 1965. The main cause of the war was the long-standing territorial dispute over the region of Kashmir, which both countries claimed as their own.

The conflict began with a series of skirmishes along the border between India and Pakistan, which escalated into a full-scale war after Pakistan launched a surprise attack on the Indian-controlled portion of Kashmir. India responded with a counter-offensive that pushed deep into Pakistan's Punjab province.

The war was fought on both the eastern and western fronts, with heavy fighting taking place in the Rann of Kutch region in the west and the Punjab and Kashmir regions in the east. The conflict also saw the first use of tanks and jets by both sides.

Despite early successes by Pakistan, India eventually gained the upper hand and managed to push Pakistani forces back across the border. The war ended on September 23, 1965, with a ceasefire brokered by the United Nations.

In summary, the main reason for the Second Indo-Pak War was the ongoing dispute over Kashmir, which had been a source of tension between the two countries since their independence in 1947. The conflict highlighted the deep-seated animosity between India and Pakistan, which has persisted to this day and continues to be a major source of instability in the region.