Answer:
Both secretaries share a large number of action scenarios, since both are responsible for foreign policy issues (but at different levels).
The Secretary of State is responsible for carrying out the foreign relations of America with the other nations, while the Secretary of Defense is responsible for everything related to the armed forces, the investment in military expenses and the operations they carry out.
Both secretaries could have differences and conflicts, since the decisions of one can affect the field of action of the other. For example, a certain purchase or sale of armaments authorized by the Secretary of Defense can trigger a diplomatic conflict with a nation (for example, if weapons are sold to Israel, diplomatic conflicts can be triggered with Middle Eastern nations).