First of all UNIVERSAL ADULT FRANCHISE
then,The Universal Declaration of Human Rights, adopted unanimously by the United Nations General Assembly in 1948, recognizes the integral role that transparent and open elections play in ensuring the fundamental right to participatory government. The Universal Declaration of Human Rights in Article 21 states:
Everyone has the right to take part in the government of his/her country, directly or through freely chosen representatives.
Everyone has the right of equal access to public service in his country.
The will of the people shall be the basis of the authority of government; this will shall be expressed in periodic and genuine elections which shall be by universal and equal suffrage and shall be held by secret ballot or by equivalent free voting procedures.
then,
International and Regional Instruments of Protection