Is it permissible to trade lands by leaving them for a period until their value increases, and then selling them? And is this considered a monopoly?

The prohibited hoarding is not the purchase of a commodity—such as land—with the intent of reselling it for profit when its price increases. Rather, the forbidden hoarding is the withholding of food and sustenance. Some scholars have extended this to include anything people need during times of high prices and severe necessity, in order to inflate its price for them. It is stated in Asna al-Matalib: "It is forbidden to hoard, which is to withhold what one has purchased during times of high prices—not during times of low prices—in order to sell it for more than its purchase price when there is a severe need. This is in contrast to withholding what one has purchased during times of low prices, which is not forbidden at all." Therefore, there is no objection to this trade.