What are the causes of bulimia?

Several causes. Bulimia is a multifactorial disorder, causes include genetic, psychological, biological, social and environmental. Eating disorders are a phenomenon of newer world with pressures from tv, movies and stress of maintaining body shape.
Many things. There is a gentic component at times, traumas of all kinds can precipitate it, especially sexual abuse and even supposedly well meaning teasing as a child can hurt to the point that an eating disorder will develop. Women are more likely to develop eating disorders. Eating disorders that occur post-partum are fairly common as well. Learning the cause and getting help asap is imperitive to recovery.