Polar is refer as Centre of power in geopolitics, power that comes from economic and military edge over the rest of the world. 

Before the fall of soviet union in 1991,There is bipolar world, whole world is divided into two blocks Democratic united state of America and Communist soviet union, These two countries are epicenter of power. By natural means the strong will fight to stay in power. Same happens in case of united states of America and soviet union. After the end of world war 2 Germany and capital berlin is divided in two parts, United kingdom united states of America and France get one part and Soviet union gets other part. and cold war starts. and with the fall of soviets union cold war end in 1991.

As the cold war ends there is no power left to tackle united states of America. This makes America superpower, This system is refers as unipolar world. 

Because of Americas excessive and unilateral use power to invade  countries. these is natural rebalance is occurring to tackles America. North Korea and Iran is making nuclear weapons, ballistic missiles.

There is rise in trade due to Globalization in countries other than Europe. rise of the Asian economies like India, china and japan takes place. GDP of china grow fast which is sufficient to tackle America as superpower in near years is possible. China is on the way to become superpower with dominance and Infrastructure projects around world. The projects like OBOR. most of the world countries are members of OBOR. The project make trade route from china to western countries by land and sea means. For Roads, ports, hydropower plants  and other project loans are given by china under this project. but the projects are only useful to china. The projects are not made with requirement of countries. the size of loan amount given by china is not bearable to countries which make countries to fall in dept. trap. The ports are developed by china, loaned by china but china loans are difficult to pay.so the port will be leased to china. This makes china powerful and countries is dependent of china.

India has growing middle class which gives people purchase power means Indian people can buy things. which India largest market whole world want accesses in India to sale there products. Rise in FDI this things gives India power.

BRICS countries Brazil, Russia, India, China, South Africa are rising power  going to stabilizing power in world. the rise in multiple power centers around world is knowns as  Multipolar world.