Survival for the whole people: build mechas at the beginning, open Gundam

[System + Iron Man + Ease] Tang Xiaofan came to the land of gods and demons, became the master of the castle, and participated in the fair and just competition of all races.
At the beginning of the advent, each castle owner will randomly obtain a unit building.
Recruit troops, plunder resources, establish a dynasty, and contend for supremacy among all races!
And Tang Xiaofan was surprised to find out.
What he randomly found was a unique unit building - [Farmer's Factory]!
Only the lowest-level unit, the farmer, can be produced!
Even so,
But unexpectedly, he actually has the system to help!
"Sir, I am your system, my name is Jarvis."
"Sir, it has been detected that your world is extremely dangerous, and the optimal solution has been given...Mark 1 Mech."
"Sir, I suggest you form a steel mecha corps as soon as possible, and start the journey to rule the mainland."
"Sir, I suggest you occupy the castle of Ugly Country as soon as possible, and make Ugly Country surrender to Dragon Kingdom!"

Main characters: Tang Xiaofan, Yi Xue,

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