Antimatter is so far the most effective strategic weapon that has been discovered: it has great destructive potential both in space and on a planetary surface, it is extremely compact even in strategic amounts and it can be produced using fairly simple technology once the basic groundwork has been laid. Add to this the possibility of antimatter propulsion and FTL weaponry, and it becomes clear that interstellar strategic warfare is quite feasible for practically all starfaring civilizations.
The attack can be made anonymously, precluding counterstrikes. Distance is irrelevant in this form of warfare; an attack can employ multistage warping to reach over extreme distances with no risk for detection. Due to the surpise element the target is unlikely to be defended, and even intelligent defenses are unable to prevent an FTL attack. All detectable targets are hance likely to be destroyed. This includes planetary bodies down to the size that can be detected by the enemy, any obvious installations and any obvious activities in the system. The only way of protecting oneself against such attacks is by hiding, either caumoflaged as inocuous objects or in empty space with low emissions.
This strategic truth has forced us to reconsider much of the long range defense plans for humanity originally developed by ICC in the 50's. The ALMANAC project is likely only the first of a series of ISOCs (Interstellar Space Operations Center), where ordinary deep space operations centers are moved into interstellar space with the intention to create hidden bases with very low detection probability. It has been estimated that as long as emission control is maintained a ISOC can remain hidden from high resolution multispectral sky scans if the distance is more than ten million kilometers, which suggests that the chance of discovery by random sampling of a one ly3 in space is less than 10-18.
The conclusion seems inescapable: to be safe from strategic attacks any starfaring civilization will need to place its installations in interstellar space where they are extremely unlikely to be found. Installations or activities in solar systems are unsafe and essentially defenseless; the best strategy is low-key activity to extract necessary raw materials which are brought back to the interstellar community. This fits surprisingly well with the Petra findings - raw materials had been extracted in a fairly well hidden outpost, which has later been abandoned and likely carefully cleaned to remove any trace of its origin.
This theory explains the Fermi Paradox: only young and immature civilizations reveal their presence and remain inside solar systems. Sooner or latter they either are destroyed in internal or external wars, or they move out into interstellar space. In the interstellar voids other advanced civilizations exist, but each hides from the others; revealing one's existence is too dangerous.