When Did I Start Getting Territorial?

I have a big problem when people invade what I perceive to be "my space" at work. This includes, but is not limited to:

1. Getting too close to me. For example: where I work, people think it's okay to come around my desk and talk to me while staring at my screen. Okay, how about no. I'm on this side of the desk, do me a favor and be on the opposite side. I'm not watching porn on the computer, but I deal with some sensitive information for clients such as socials, income, addresses, and I'd rather you not have your face in it.
2. People picking up things off my desk. I have a few things on my desk at work. The only reason I have anything is because those things are important: my thermos, a picture of my husband and me, and an iron rose. That's it. Three things. People decide picking up one of these three objects is cool. Well, it's not.
3. Siting in my chair without asking if it's cool. Look, this is my desk. This is my chair. Why is it when I get up, suddenly it's free game to people WHO DON'T WORK IN THIS OFFICE?! Oh hey, lookie here, I got up to do something and you're just siting in my chair, looking up something on my computer, and you didn't bother to take a second and ask "Can I use this a minute?". Rude.

These are not nit-picky in my opinion, these are common sense things. Is there an implied barrier? Good. Stay on your side. Does this belong to you? No? Then don't touch it. Did you ask to use that? Then guess what, you can't use it. Follow that simple guideline, and I won't need to end you.