Complex sentence: The Viceroy of India had already warned the Emir of approaching "German agents and hired assassins", and the Emir had promised he would arrest the expedition if it managed to reach Afghanistan.
Split into simpler sentences: The Viceroy of India had already warned the Emir of approaching "German agents and hired assassins". The Emir had promised the Viceroy to arrest the expedition if it managed to reach Afghanistan.