Sauerkraut is shredded cabbage in the presence of 2-3% salt, acid-forming bacteria thrive and convert sugars in the cabbage into acetic and lactic acids, which then act as preservatives. So it is already preserved.
It means to keep stay united. A good example of this was the American War Between the States also known as the Civil War. The war was fought to keep the states united into one country instead of two...
Well, the word preserve can mean a few things. In general it means to keep something for a long period of time. A preserve can be like an Animal Preserve... a place where animals can go to be safe...