Complex sentence: Before the invasion was set to begin, news had reached India that the Persians and Russians had abandoned the siege of Herat and many British officers believed that there is no longer a reason to invade Afghanistan.
Split into simpler sentences: Before the invasion was set to begin, news had reached India that the Persians and Russians had abandoned the siege of Herat. Many British officers now believed that there is no longer a reason to invade Afghanistan.