Number 2 seems to spark my interest most. 

Heres my ideas for a Civil War type-
1. Civil War Plots(3)
Andrew and Claira- Andrew and Claira have been friends since they were kids and as they grew older it became something more. The loved each other, but Claira's parents refused to agree to their relationship because Andrew was just the son of a lowly wood cutter, where as her father was a high offical of Kentucky. Even so, the two had made plans to get married secretly. But, because a tip given to her parents by one of Claira's friends, they found out. Not wanting to have their daughter married off to Andrew, they move and tae her with them up north one state to Ohio. Three years pass and the civil war starts. Andrew joins the Confederate army. Claira on the other hand tried to join as a nurse on the Union and gets denied. Despreste to help with the war, she desguises herself as a man and joins the Union arm as a solider. Though unfortinantly, during her third battle, she gots shot and wounded. Andrew, ordered by his supiorers to kill the Union survivers, goes to the feild to do as he is told and find none other then Claira.
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Michael and Haily- Michael is the son of poor cotton farmers from Georgia and Haily is the daughter of a couple that pick oranges in Flordia. Both joint eh war under the confedrate army, Michael as a Solider and Haily as a nurse. When Michael is wounded, he is placed in the infirmary where Haily is put in charge of taking care of the young man, who has one small flaw. Thanks to growing up with a father who looks down on women, he does the same and seems to have nothing good to saw to the girl who is taking care of him.
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Samual and Willow- Marching from battle feild to battle feild can be rather tiring. Espcially in the middle of the summer. And sleeping in tents on the ground with close to nothing dosn't make it any better. So, when you have hardly anything to drink and a well come into sight, it is a very hopeful thing. That is, until you see it is on southern farm lands. Samual, as a northern solider, at first dosn't really know what to do at first. It is either take a risk and get a drink or go thirsty for another few hours. But, he takes the risk, sneaking up to the well. Hearing footsteps though, he hides and that is when he spots beautiful Willow, the daughter of the farmers, fetching water. Setting one bucket down and turning to fill another, Sam sees his chance and sneaks out to take the bucket of water. But Willow catches him doing so and confront the young man about doing so.

Heres one I have based on Native Americans:

2. My idea was that there are two tribes at war over land because, with the Englishmen move in to the Americans, they start takig land for themselves, making good farming lands hard to come by. But to make matters worse, Tribe1 is angery with Tribe2, because to get more land, the cheif of Tribe2 married a English Woman. Years pass and the cheif of tribe 2 has a daughter who is very curious. The daughter often goes off into the woods unattended. As a child she did this, and when doing so, met a young boy around her age, maybe a few years older. She always followed him around like a lost puppy, him calling her the 'blue eyed demon' and always telling her to leave him alone, yet always protecting her when dangers came around. A year passed of them going through the woods together, going through the same things, him making fun of her blue eyes and telling her to go away, yet keeping her around and her clinging to him all the time.

Though, after that first year, a few warriors followed the princess into the woods and seeing her not just being around a boy from another tribe, the cheifs son, but her acting as though she was in love with the boy. The second tribe's warriors came out and at the same time so did te first tribes. They fought and the two children were snatched from each other and taken back home.

Twelve years passed and the childen almost completely forgot each other. The young boy, after his father's death, became cheif, and the girl became engaged to the greatest warror from her tribe. 

Though the boy is cheif, still being in his late teens, he rebels quite a bit, going into the woods alone just to spite the elders. He hunts, not just animals, but people from he warring tribe. He every once and a while crosses onto tribe2's land and kills someone from the tribe.

One day while he was doing so, he sees a person and attempts to shoot them with his bow and arrow, but missed by a few inches. The person ran and he chased after them, knowing if he didn't catch them and kill them before they got back to the village they would tell their cheif and start a whole other battle. He finally catches them, dragging the person onto his lands so killing them would technechally be justified.

He grabbed his dagger, ready to kill her, but to his suprise this wasn't just any girl from that tribe. She was the cheif's daughter, the blue eyed girl he had once been so fond of. But it was too late to let her go because a few of his warriors found him. Unable to let her go, but not willing to kill her, he forces her back to his own village, telling his people that he's planning on using her to get her people's land, when really he just wants her around.

But, as if continuing like they were when they were kids, he treats her like he hates her, still calling her 'blue eyed demon' but instead of that making her want to be around him more, like he expected it to because thats how it was when they were kids, the more he is cruel to her, the more it seems to push her further from him. Now he has trouble trying to keep her close to him because he dosn't know any other way to treat her, and at the same time, her tribe is plotting to get her back.

Anyway, so that is the idea, but I do have an extra idea that can or can't be added. Back in those days, Natives believed everyone had a animal spirit, so what if the males in the tribe1 or both tribes could turn into their spirit animal(like a hawk, tiger, wolf, ect). Again, just an idea.

Heres one for Revolutionary(this ones short. I was lazy XD) :
3. Basically I want it to be either that the British solider coming into one of the colonies and his the leader of his regiment forces the girls family to host the solider thanks to the quartering act. Either way, the solider falls for the girl, yet doesn't understand why she supports the Americans having their own country, which causes problems.

4. My mermaid idea would be that the mermaids, in order to stay young, drain a human's life. This done through, of course, kissing the human and dragging them under the water(known as the 'kiss of death'. Sometimes the mermaids will also mate with the humans before finishing them off as there are only female mermaids[in this rp anyway]). Well, a very smart Pirate Captain(who may or may not have a history with mermaids. I'll discuss that with you later if this is chosen) goes afloat in a row boat, not too far away from his ship, where a mermaid is lead to believe he will be an easy target. The mermaid lures him into a kiss, only when she drags him into the water, he manages to snap out of the magic of the kiss and places a dagger to her neck, forcing her to come up to the row boat with him, finding the mermaid's tail turns to legs when out of the water(this may or may not known by anyone until then depending on certain factors of the Captains past). The Captain forces the mermaid girl onto his ship and into his cabin wher he is determined to find answers or in the very least some some way to use the first ever captive mermaid to his advantage against his enemies or for monetary gain.

Heres an extra plot not really related to any history at all:
5. This is kind of a idea rather then a plot. 
I was thinking that there is either a robot who thinks of itself as human or a Android(human body but computer brain) who doesn't like living the life of a machine. The world that this is based in is a world where humans have been wiped out by the robot looking humans, but the only way to tell a robot from a human is that the robots have a barcode(from when the robots had been made) tattooed on their arms. But there is a group of humans and in hiding. The humans spend time capturing robots and taking them apart, trying to learn how they think and their weakness so they can shut the robots down for good. Long story short, he/she ends up capturing the Android when he/she wanders into his/her hide out and the story takes off from there.
Also, while I was in the shower(which is where I do my thinking for ideas) I had another idea for this plot. What if the Android , when it had been fully human had been with the rebels? Like she/he fought against the robots with them and learned how to fight really well? And was captured, taken by the robots, where the robots changed him/her. Took the human's bones and replaced the with metal, and replaced her/his brain with machinery and maybe his/her eyes for better for use of surroundings. But she/he still looks the same as before, but has no memories thus far of his/her human life. So when the Android comes upon the hideout after leaving the robots, the human, who may have been in a relationship or just really good friends with the Android secretly loving him/her when he/she were still human, stops the other humans from killing it and starts trying to find ways to get the Android to remember and tries to get it used to living with humans and keeping the humans from killing it.

I'll be up for your number two, or any of the ones I've listed. I'll allow you to make the final decision.