Given the fact that gravity is the weakest of all forces, how does a gas cloud manage to collapse on itself under gravity and start a fusion reaction, outweighing the electromagnetic and nuclear forces between atoms? Even if the mass is greater, it would mean that the electromagnetic and nuclear forces between atoms would also be greater. How does gravity overcome these forces?
The unique thing about gravity is that it is always attractive. Your intuition would be correct if the gas cloud was made purely of electrons, for example, as then the electromagnetic repulsion would be much greater than the gravitational attraction. But because there are both positive and negative charges in the gas cloud, the electromagnetic forces cancel out over long distances. Eventually the gas cloud can accumulate so much mass that it can overcome the other forces, despite gravity's relative weakness at the inter-particle level.