Let me just question the battle strategies of the Wandenreich in their war against the Soul Society, which is pretty much over at this point.
1: Attack with no warning.
By giving the Shinigami a warning prior to the main event, the quincies only managed to increase the chance of resistance, as well as increasing the battle power of one sternritter by a small amount. Had the Wandenreich simply started with all 26 Sternritters materialising in Yama's office and beating the crap out of him, there would be much less danger for the Quincies.
2: Plan your battles prior to invasion
The Wandenreich clearly has information on the abilities of all the captains. They should be able to plan battles beforehand. If, rather than the Sternritter appearing in random locations, each captain was confronted with one or two sternritters who's powers could provide an easy victory, then the war would be much quicker.
3: Use your Superweapon right at the start
I promise this will be the only Gremmy point on this list.
Here is the premise: It's a lovely day in the Seireitei. The captains are preparing to have a tea party to celebrate the 18th month anniversary of Aizen not killing everyone. Then, a little kid with a raincoat shows up, and drops a meteor on them. The Seireitei is destroyed, The Wandenreich rises in it's place. The end.
4: Gremmy does everything
I lied. Gremmy can create life. Using point 2, he can create his own soldiers to perfectly counter the captains for those who can't allready be one shotted by a sternritter.
5: Bring your Arrancar Army
Even an ordinary run of the mill Numeros arrancar can fight better than a worthless Soldat. If Yhwach has used his arrancar army, he would have... Wait, that wouldn't really change anything. Still, he should have used them to bolster the fighting force.
6: No Auswahlen
Possibly the worse part of Yhwach's plan is to have his elite guards running on approximately 1% Power for the first conflict. Instead of restricting their powers so Robert Accutrone, Candice Catnipp and Meninas McAllon have to die, how about you... Don't Do That! Have the elites at full power, or at least able to use their schrifts before sending them into combat with the Zero Squad
7: Zombie Thor of Doom!
Step 1: Kill Gerard Valkyrie. Step 2, Ressurect Gerard Valkyrie with Gissele Gewele. Step 3, activate "The Miracle". Step 4: Gerard starts juggling planets.
In short, make sure that situational powers like The Miracle are allready active prior to invasion. Although in fairness, i can see Yhwach overlooking a plan as stupid as this one.
8: Be Patient!
The sealed kind of the quincy blah blah blah 900 years blah blah blah 90 year blah blah blah 9 years blah blah blah power. In short, after 999 years, Yhwach get's his Almighty Eyes back. That 999 years ended in his fight with Ichibe Hyosube, about 1 week after the start of the war. If he had just waited that week, Yhwach could have effortlessly demolished the Seireitei himself. When the Zero Squad showed up (Breaking the Soul Palace Barriers in the process), Yhwach would be able to defeat them as well, before going up to the soul king's palace and becoming God with zero casualties on the quincies side. Final score, Infinity - Nothing, to the quincies.
1: Attack with no warning.
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2: Plan your battles prior to invasion
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3: Use your Superweapon right at the start
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Here is the premise: It's a lovely day in the Seireitei. The captains are preparing to have a tea party to celebrate the 18th month anniversary of Aizen not killing everyone. Then, a little kid with a raincoat shows up, and drops a meteor on them. The Seireitei is destroyed, The Wandenreich rises in it's place. The end.
4: Gremmy does everything
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5: Bring your Arrancar Army
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6: No Auswahlen
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7: Zombie Thor of Doom!
Step 1: Kill Gerard Valkyrie. Step 2, Ressurect Gerard Valkyrie with Gissele Gewele. Step 3, activate "The Miracle". Step 4: Gerard starts juggling planets.
In short, make sure that situational powers like The Miracle are allready active prior to invasion. Although in fairness, i can see Yhwach overlooking a plan as stupid as this one.
8: Be Patient!
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