A federal system of government is characterized by a division of powers between a central authority (Union/Federal government) and constituent political units (States/Provinces). This inherently involves relations between the Union and the States. Furthermore, states within a federation often have interactions and potential disagreements among themselves, requiring mechanisms for inter-state relations. Finally, in a system with divided powers and multiple levels of government, disputes are bound to arise, necessitating an independent judiciary or other mechanisms for conflict resolution. The points listed (1, 2, and 3) are fundamental aspects of a federal polity. There is no point 4 listed in the question.