Factors behind generation of monopoly:

The main causes that lead to monopoly are:

i) Ownership of strategic raw materials or exclusive knowledge of techniques of production.

ii) Patent right on a product or on the process of production.

iii) Government licensing or the imposition of foreign trade barrier to restrict foreign competitors.

iv) The size of the market may be such that it cannot support more than one seller.

v) The producer may exhibit increasing returns to scale (as it happens in transport, electricity and communication), as a result, cost of production declines when a firm operates on a large scale and this might throw out other producers who are unable to complete with the low cost firm.

vi) Practice of limit pricing may prevent new entries in a market and can create monopoly. 

Thus, in monopoly market,

i) there is a single seller

ii) close substitutes of the product do not exist

iii) there is no free entry and exit as in perfect competition.