Catalyst Game Labs has some new BattleTech PDFs available to order over in their webshop.
From them to you:
Historical: Wars of the Republic Era describes the border conflicts that inevitably erupted in the decades after the Word of Blake Jihad. Covering the largest of these conflicts in particular—including the Second Combine-Dominion War, the Victoria War, and the Republic of the Sphere’s own war against the Capellan Confederation—this book provides a hard look at the early years of what would come to be known as the Dark Age Era.
In 2765, the Star League Defense Force was the greatest military ever assembled, unparalleled in numbers and technological prowess—but it was not alone. The House Lords and the rules of the Territorial States in the Periphery each amassed armies of their own. While none of these powers alone could challenge the sheer size and might of the SLDF, each stood ready to defend their own interests against the avarice of their neighbors.
Field Report 2765 AFFS describes the state of House Davion’s Federated Suns just before the events described in Historical: Liberation of Terra, Vol I, including the overall military and logistical condition of one of the Great Houses that would eventually survive the collapse of the Star League and face a new age of endless war.