Complex sentence: Remote, with the nearest rail connection being at Phitsanulok, a half-day's drive away, Phetchabun's main asset was its suitability as a mountainous fortress; moreover, the site was located in a region where the majority of the Thai army was based.
Split into simpler sentences: Remote, with the nearest rail connection at Phitsanulok, a half-day's drive away, Phetchabun's main asset was its suitability as a mountainous fortress. Moreover, the site was located in an area where the majority of the Thai army was based.