Complex sentence: The autonomous community is based on the Statute of Autonomy of the Basque Country, a foundational legal document providing the framework for the development of the Basque people on Spanish soil, although the territory of Navarre was left out and made into a separate autonomous community.
Split into simpler sentences: The autonomous community is based on the Statute of Autonomy of the Basque Country, a foundational legal document providing the framework for the development of the Basque people on Spanish soil. Not withstanding this spirit, the territory of Navarre was left out and made into a separate autonomous community.