Under what conditions might an Rh- blood develop Rh antibodies

explain in easy words please

There are only two conditions that can cause Rh- blood to form antibodies:

1. when an Rh- mother is carrying an Rh+ baby

2. if an Rh- person receives an Rh+ blood transfusion

What happens is the Rh+ blood entering into the Rh- bloodstream gets interpreted by the circulatory system as a foreign body so the Rh- blood produces antibodies to "fight" the foreign matter. This causes the blood to clump leading to blockages of blood vessels which can lead to heart attacks, stroke, death of the baby (in the case of pregnancy) and death of the person (in case of transfusion).