When a constitution requires a special organ or a more difficult amendment procedure, such constitution is applicable in which system of government?

A constitution that requires a special organ or a more difficult amendment procedure is known as a rigid constitution, and this type of constitution is most closely associated with a federal system of government.

In a federal system, power is constitutionally divided between the central (federal) government and the component units (states or regions). To protect this division of powers and prevent either level of government from unilaterally altering the constitutional arrangement, the constitution is made rigid - that is, it requires a special, more complex procedure to amend. Typically, this involves:

• A two-thirds or three-quarters majority vote in the national legislature
• Approval by a specified proportion of state or regional legislatures
• In some cases, a special constitutional convention or referendum

For example, Nigeria's 1999 Constitution (a federal constitution) requires a two-thirds majority of both the Senate and House of Representatives, plus approval by at least two-thirds of the 36 State Houses of Assembly, to pass a constitutional amendment.

Parliamentary and unitary systems may use either rigid or flexible constitutions. A confederation typically operates through treaties rather than a single constitution. The federal system, however, inherently requires rigidity to safeguard the balance of power between levels of government.