How demons appear?

[Explorer]

It is commonly known that the Twisting Nether is separated from other worlds by some sort of a barrier - in order to summon a demon, a portion of power should be spent, proportional to the demon's strength - to summon a simplistic imp you only need to spent some mana, and Sargeras, yes? All the power of the Well of Eternity. KJ takes Sunwell to be able to come through, etc. Sooo, the questions are:
1. Aegwynn and Avatar of the Sargeras. How did it appear??? It is simply said that it - BAM! - and came along, though it might be an avatar, it would definetely cost some energy to summon. Who summoned te avatar and a group of demons there?
2. How did the Lich King came to Azeroth? KJ just "hurled" him there, wtf? Of course, LK gained power from creatures he killed, but to be able to distantly drain someone you need a seroius amount of starting power, no? If they cam come to Azerot so easily, why make that circus with Dalaran for Archimonde or Sunwell for KJ? And if they need some serious support from this side, WHY is in never mentioned?
P.S. - don't understand those who yell - "in the next expansion infernals just start to rain all over Azeroth, demons swarm through the portal...." Isn't it an obvious nonsence? If they can just falls wrom the sky, why would they ever bother with the Highbourne, orcs, Scourge? Is that so difficult to understand? They need a powerful gate and constant energy support to be able to enter.... And where can you see one?

[Sierra85]

the simplest answer is always the best, magic.

[Verdugo]

Dont look for depth in warcraft, you will only find countless plot holes.

[Heenk]

How birds suddenly appear?

[Deleted]

It is commonly known that the Twisting Nether is separated from other worlds by some sort of a barrier - in order to summon a demon, a portion of power should be spent, proportional to the demon's strength - to summon a simplistic imp you only need to spent some mana, and Sargeras, yes? All the power of the Well of Eternity. KJ takes Sunwell to be able to come through, etc. Sooo, the questions are:
1. Aegwynn and Avatar of the Sargeras. How did it appear??? It is simply said that it - BAM! - and came along, though it might be an avatar, it would definetely cost some energy to summon. Who summoned te avatar and a group of demons there?
2. How did the Lich King came to Azeroth? KJ just "hurled" him there, wtf? Of course, LK gained power from creatures he killed, but to be able to distantly drain someone you need a seroius amount of starting power, no? If they cam come to Azerot so easily, why make that circus with Dalaran for Archimonde or Sunwell for KJ? And if they need some serious support from this side, WHY is in never mentioned?
P.S. - don't understand those who yell - "in the next expansion infernals just start to rain all over Azeroth, demons swarm through the portal...." Isn't it an obvious nonsence? If they can just falls wrom the sky, why would they ever bother with the Highbourne, orcs, Scourge? Is that so difficult to understand? They need a powerful gate and constant energy support to be able to enter.... And where can you see one?

The Legion already has agents on Azeroth left over from the War of the Ancients I guess who can summon more in as needs be. Also, something that I feel is important is that in Stormrage, the Rift of Aln is described as opening up into the Twisting Nether. This is certainly true in the Emerald Dream and may well be true in the physical world as well.