Epic space opera movie retellings with a lot of politics and strategy, sharing common themes of intergenerational divide.
Mobile Suit Gundam I is the first in a trilogy that compiles episodes of the Mobile Suit Gundam television series for quicker viewing. Overture to a New War is both a prequel and a remake of the first couple of episodes of the Legend of the Galactic Heroes OVA. Both are retellings of previous material but neither are by any means replacements, as the things they add/change serve to complement their existing source material.
Both depict the tragedy of war, the longing for and the loss of loved ones
in such harsh times, effecting both civilians and soldiers. In Mobile Suit Gundam I, this is exemplified with the invasion of Amuro's home space colony Side 7 and the relationship between Garma and Icelina on the Zeon side. In Overture to a New War, we have the trio of Yang, Jessica and Lapp on the alliance side as well as the trio of Reinhard, Annerose and Siegfried on the imperial side.
Mobile Suit Gundam I has the young ragtag crew of the White Base, who are shown to have combat potential, being ordered around as decoys by the Federation higherups whereas Overture to a New War depicts Yang and Lapp being held back by their older superior's stubbornness reliance on old strategies for space warfare.
Most importantly, the greater scope conflict in both movies are between a democracy and an autocracy; in Mobile Suit Gundam I, the Principality of Zeon, ruled by an absolute monarch, uses the rhetoric that they are freeing their fellow space colonists from the corrupt but democratic Earth Federation that had oppressed them for so long. In Overture to a New War, the conflict is between the autocratic Galactic Empire (the founder became emperor through bringing order to a decadent galaxy) and the corrupt but democratic Free Planets Alliance that began as rebels. 
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