Complex sentence: As part of his attack Ivan burned the field and laid waste to roughly 90 percent of the arable land surrounding Novgorod that coupled with the crop failures of the years before, would create a massive food shortage (and cause supply in the Livonian war).
Split into simpler sentences: As part of his attack Ivan burned the fields, laying waste roughly 90 percent of the arable land surrounding Novgorod. Coupled with the crop failures of the years before, this would create a massive food shortage (and cause supply in the Livonian war).