The main cause of Blood Coagulation is damage to the inner lining of the Blood vessel. When the structure of the artery is damaged, it exposes subendothelial tissues, which activate platelets and bring about extensive thrombus formation. Other causes of Blood Coagulation include injuries, surgery, childbirth, cancer, obesity, and the use of oral contraceptives. Blood clotting can also be caused by various medical conditions such as deep vein thrombosis, heart attack, stroke, and pulmonary embolism. The main cause of Blood clotting is when the inner lining of a Blood vessel is damaged.