Complex sentence: In the 10th century, the territory of Pressburg (what would later become Pozsony county) became part of Hungary (called "the Kingdom of Hungary" from 1000) and developed as a key economic and administrative centre on the kingdom's frontier.
Split into simpler sentences: In the 10th century, the territory of Pressburg (what would later become Pozsony county) became part of Hungary (called "the Kingdom of Hungary" from 1000). It developed as a key economic and administrative centre on the kingdom's frontier.