Continuing from the last book (Rally Cry), Union Forever returns us to the planet Vallenia and the Horde. See my previous review for details on how the troops arrived and their first battles. Also please note, these reviews are a general synopsis of the book so do abound with SPOILERS.
Union Forever introduces us to two new races of humans – the Roum and the Cartha – descendents of the Romans and the Carthagians respectively that had been transported to Vallenia during the Punic Wars (Rome and Carthage had several significant battles during 264 to 146 BC. At the time, they were probably the largest wars that had ever taken place. Rome during these wars was NOT a seafaring power as was Carthage and one of the most ambitious and noteworthy aspects of this conflict was the way in which the Roman legions copied a captured Carthage warship and created a Navy using it as a template).
After the climactic battles of the previous book, the Roum were able to defeat the remaining Tugar hordes that were attacking and thereby saved themselves from having to pay the customary tribute to the horde. The soldiers of the 35th Maine along with Andrew Keane and Kal (the president of the Rus) strike up an alliance with the Roum and extend their rail line into their territory.
Further south, other things are happening and the Merki horde have learnt of the defeat of the Tugar. Pressed as they are by the Bantag horde themselves, they need to come up with a significant win and with the Cattle starting to fight back they need to do so fast. The leader of the Merki Horde, Jubadi, has decided it is up to him and his Horde to put down the cattle that dared to rise up against the “Chosen Race”. Jubadi summons Mutza (the leader of the remanants of the Tugars) and together they devise a plan to destroy the Rus and all the other Cattle that have chosen to fight back. Mutza and Jubadi do not trust each other, but they are forced to work together due to Mutzas realization that the Tugars can be destroyed outright and Jubadi’s fears of the Bantag. Both are united in their hatred of Andrew Keane and the 35th Maine however!
Jubadi has managed to capture Tobias Cromwell (who deserted along with his ship at the end of 1st book) and is utilizing his skills and knowledge to arm the Carthagians and 
convert them into a steam and gunpowder based society in an effort to compete against the Rus empire. With the Carthagians forced to work with the Merki, they design and deploy a mix of Civil War era weapons – cannon, ironclad ships, muskets, all the tools they believe they will need to wipe out those to the north.
With a cunning plan in place to split the forces of the fledgling republic, an attack is launched upon Roum by the Carthagians with Tobias Cromwell at the head. Once the forces are committed, it is only Vincent Hawthornes battalion that is able to fight off the stronger Carthagian forces and Marcus (the leader of the Roum people) is forced to call upon the alliance to send forces to relieve them from the siege. In response to the plea for help, Rus sends much of its army to Roum upon the recently built railroad leaving Suzdal relatively defensless.
After much privation and hardship, Colonel Keane arrives with his forces at Roum and manages to relieve the remaining forces of Vincent Hawthorne. Vincent and Marcus had managed to survive in Roum by releasing the slaves of the Roum empire and with these added forces they were able to defeat the Carthagians and Legion forces that had been attacking. Once Keane arrives though, Cromwell sets in motion the second part of his plan and with a small force of men, they destroy the rail line connecting the two cities together stranding the forces of Rus in the Roum. With a taunting message to Keane, Cromwell takes his naval forces and sets off to attack Suzdal.
Realizing quickly that an overland forced march back to Rus would take much too long, Keane decides to do the unexpected and build a Roum navy to counter Cromwell. Because they knew that they could not outmaneuver the Carthagians with their increased familiarity of shipboard battle and improved ships, the Roum forces decided to build ships with a “Corvus” … basically a bridge that would connect together two ships allowing the fighting forces of one to swarm onto the other (this is very similar to the tactics employed during the Punic wars also).
Utiilizing the engines from the trains that had initially transported the Rus forces to Roum, the Republic forces field a significant armada of ships and set off to fight against the Carthagian forces led by Cromwell. While this was happening, Mikhail had led an uprising in Suzdal and had managed to capture the city allowing Cromwell and the Merki access to it. The Merki had sent one Umen of troops (all that they could release due to their ongoing struggles with the Bantag) towards Suzdal to ensure that it was destroyed and did not cause any future problems.
Realizing that the Merki are on their way, the remaining loyalist forces attack Suzdal again while Keane’s naval forces deploy against Cromwell. After taking desperate losses both of men and ships, Keane’s forces are able to finally win their way to victory only after Cromwell realizes that the Merki had intended to betray him after all and elects not to fight.
Similarly, the loyalist forces are able to retake the walls of Suzdal just as the Umen of the Merki Horde is approaching and with that vantage point are able to ensure that Suzdal is safe.
With victory assured, the men and women of the fledgling republic feel secure and safe … however … just as they start to celebrate, a Merki blimp flies over and destroys the ammunition dump for the Rus forces. The war is far from over and the stakes are continuing to increase!