There are 2 diffrent things. There is the spirit world. The issue with the aliens, is that you find in every civilazation of the the world that there was an interraction with so called Gods. Because mankind was in a primitive stage, they considered those aliens as Gods. The Summerians called them Anunakki, Gods that they came from the sky and gave knowledge to the world. Greek mythology again had the 12 Gods that gave knowledge as well. Inkas & Maya the same, the Indian Epic of Mahabharatra, dated 5000 years ago, speaks about Gods that fought a war in the sky,(same idea with the Hellenic war of the Titans)and one God have used a weapon that killed hundreds of thousands with just one explosion(nuclear bomb) In the region that this war took place, in India, they found high radiation, since radiation can be traced for thousands of years.
What they are teaching us in History it is not the entire true. There was an advanced civilization on Earth, but destroyed. Take for instance the building of the Pyramids in Egypt(there are bigger ones in China). Even with the technology we have today we cannot build them. But the Egyptians build them in a short time, and still we cannot understand how they did. Is just a puzzle with missing peaces. Put them together and you will get the picture.