Explanation:

Muhammad bin Tughlaq or the 'wise fool' changed his capital from Delhi to Daulatabad for the following reasons

As the Deccan was very far from Delhi and he wanted to strengthen his control over the Deccan.
He wanted to save himself from the threat of Mongol invasion from North west India
An interesting theory by Ibn e Batuta states that MBT did not like his life in Delhi as he got threatening letters from people in Delhi, criticising his rule. So he wanted to lay waste to Delhi and punish the people who were threatening him. Though this theory is not accepted by later historians, it still is interesting.
He chose Daulatabad which was approximately equidistant from both, the northern and southern extremes of his empire and then all of Delhi was ordered to leave for the new capital.

The 1500 km shift took place in the sweltering summer. For the benefit of the travellers MBT provided rest houses on the way but many people died on the way. Many others felt homesick as they missed their age old homeland.

Few years later, MBT decided to scrap the plan and decided to move back to Delhi as he found that it was difficult to control the north from Daulatabad. Once again the whole population was told to shift back to Delhi.