Complex sentence: The United States was amongst the first nations along with Iran and few others, to establish relations with Pakistan in the late 1940s, but since then, relations have been centered around the United States' extensive economic, scientific, and military assistance to Pakistan.
Split into simpler sentences: The United States was amongst the first nations along with Iran and few others, to establish relations with Pakistan in the late 1940s. Since then, relations have been centered around the United States' extensive economic, scientific, and military assistance to Pakistan.