This starts out as a "Twilight gets banished for attacking Cadance, who is actually Chrysalis in disguise" sort of fic. Some time after discovering that Twilight was right all along (and all the guilt, regret and angst that this involves), Princess Celestia receives reports of the Crystal Empire's return and sends Cadance and Shining Armor. After not recieving any news from Cadance and Shining Armor for some time, Princess Celestia then decides to investigate, with Princess Luna, Spike, and the remaining members of the Mane Six along side her. When they learn several jarring facts:

A) Twilight made it to the empire first, found the Crystal Heart, defeated King Sombra, and became the new Crystal Empress.
B) After Twilight shared her tale of woe with her new subjects, compounded by the fact that the Equestrian Princesses were responsible (albeit indirectly) for them being stuck in a pocket dimension with an ethereal tyrant for a thousand years, the Crystal Ponies have a rather negative opinion on Equestrians.
C) News of the Changelings defeat has yet to reach the Crystal Empire, so as far as anyone knows, Equestria has become the Changeling's puppet kingdom, Cadance is actually Queen Chrysalis, and Shining Armor is still under her thrall.
D) Shining Armor and Cadance were captured and detained by the Crystal Guards almost as soon as they entered the Empire proper. Shining Armor being kept under observation in the castles medical wing in order to properly ascertain the extent of Chrysalis' mind control, as well as any potential side-effects such long-term control may have. Cadance is under heavy guard in the palace dungeons, awaiting trial for crimes against Equestria and against the Empress of the Crystal Empire. All attempts at negotiations and pleas for reason from the two are being written off as Changeling tricks.
E) The Empire if gearing up for war. The goal: to liberate Equestria from the Changeling scourge, and annex the kingdom.

I recommend putting a link to this page on the Canterlot Wedding Blues group.

I can see that happening and when the others learn that their actions are the cause of Twilight making war plans and realizes that twilight thinks they are changelings they would be hesitant to fight because the war is their own fault. Twilight has a good chance of winning a fight. Luna won't interfere unless it is darkness controlling twilight to save the one that saved her from herself. Celestia wouldn't fight because she cares about Twilight. And the elements of harmony won't work because Twilight is doing what she believes is goo for harmony.

So it would place them in a corner with the only options of surrender or fight.

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And, as a potential subplot, the real Chrysalis could take advantage of the situation to place agents within both sides of the conflict in order to ensure the two nations actually do go to war, the plan being that, with both sides weaken, the Changelings would be able to conquer both Equestria and the Crystal Empire.

For those interested, here's the link to the original post: https://www.fimfiction.net/group/200588/canterlot-wedding-blues/thread/293051/idea-seed-twilight-conquers-the-crystal-empire

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Yes I am having a plan to do that but which Mane 5 should be the changeling? And do you have a name for a guard in both armies?

Mane 5 Fluttershy or applejack?

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You couldn't really go wrong with either one, if you ask me.

Personally, none of the Mane 5 should be the Changeling (in my opinion, the security around them post Changeling invasion would insure that not even the most skilled Changeling agents would be able to get within twenty feet of them.). I was thinking more along the lines of the lesser nobility being replaced (not important enough to warrant high security, but influential enough to sway things in favor of the Changelings.)

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I prefer A.

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A isn't a choice, I'm just laying out the setting.

6247372
oh I see.