Path of the Thundering

Some Barbarians find their power, their tremendous strength and their unending fury from connections to their Gods and Deities; Others find it in connections with the natural world around them and the many different forms this world may take; Some claim their powers are blessings from Spirits and entities beyond a simple, mortal life.
The Thundering Barbarians find their homes in no such places. Like the Battleragers of the Dwarven Clans beneath the Mountains and the Berserkers from their wild lands and fringe-realms; when these Barbarians make their treks down from their frozen Peaks, great and ever-reaching Steppes, from across their Savannahs or horizon-reaching Plains- for whatever reason or whatever their calling may be- The Skies shake and the Earth quakes before them, cowering away from their world-moving power.
They walk with the steps of a thousand soldiers striding into battle and roar with just as numerous a power. As lightning lights up the sky and cacophonous thunder follows suit, flashes of steel are avouched for by mighty bellows and rumbling footfalls of armies.

Thunderous Footfalls

You walk with the Power and Thunderous booms of an army 1000-strong. Your footfalls echo through the sky and travel through the earth.
Once you begin your rage, your footfalls shake the ground you walk upon and even your mere presence in rage continues this affect- creating an area of unsteady earth around you.
You produce a constant aura- Size: 10ft radius- around yourself, causing difficult terrain within this aura area.

Also: While you are raging, you can channel your strength and ferocity into one great boom. You raise your leg and Stomp down with all your might- As an action, whilst raging, you force enemies- within Size: 10ft radius on the ground- to make a DEX saving throw. On a success, no effect occurs. On a failure, the failing target falls prone and takes damage equal to your Rage Damage Bonus.
At higher levels: 6- This ability deals 1d6 Bludgeoning damage to each target that fails their save. At levels 10 and 14: This damage increases by another 1d6.

The aura affect is passive, occurring always as you rage. You may decide if any creatures are not affected by this difficult terrain.
The action affect may be used an equal number of times to your Proficiency Bonus. 
Size of Difficult Terrain aura and Action Stomp affect increases by 5ft each at: Level 14.

The Pounding Gale - Forceful Strikes

You walk with unstoppable might of the wild and powerful Winds, that tear across the Plains into tornadoes and swirl around Mountains into blizzarding storms. Your fury surges you forward with the speed of a Gale Force winds and turns your weapons and your body into the boom of Thunder, itself. You gain the ability to break the walled lines of the enemies before you and to charge at them with even greater speed.

Once per turn, when you strike an enemy with your Weapon or an Unarmed Strike, you can knock a creature back 5 feet per each bonus to your Constitution modifier(Minimum of 1 for 5 feet knockback). They can be knocked backwards or horizontally for this distance.
An enemy struck by this Special Action, whether you are raging or not, if they collide with another Enemy Target or an Obstacle, takes extra damage equal to your Rage Damage Bonus.

If the knocked back Target collides with another Enemy due to this ability, then the original Targeted Enemy stops. The Collided Enemy must then make a DEX saving throw. If they succeed, they are only knocked back 5 feet- this Target will not take damage if it collides with an Obstacle but can still collide with another Target.
If the Target fails, they are knocked back the full remainder of the Knocked Back distance that the original target still had left to travel(Minimum of 5 feet) and the Target takes Damage equal to your Rage Damage Bonus.
This effect repeats itself if multiple enemies in a row are Collided into, as a result of this Special Action Feature, until the full Knocked Back distance has been travelled or until a Knocked enemy collides with an Obstacle.

The DC for this Save = (8 + CON + Proficiency)
You can use this feature twice per Long Rest.

The Pounding Gale - Surging Steps

You walk with unstoppable might of the wild and powerful Winds, that tear across the Plains into tornadoes and swirl around Mountains into blizzarding storms. Your fury surges you forward with the speed of a Gale Force winds and turns your weapons and your body into the boom of Thunder, itself. You gain the ability to break the walled lines of the enemies before you and to charge at them with even greater speed.

When you reach Level 6 in this Subclass, you also gain an extra 5 feet of movement per turn.

Roar of the Howling Gods

You build a great deal of energy within you and fury rushes through you. As an Action, you bellow and cry-out, as though lightning had struck inside your soul and thunder boomed out of your mouth. With this cacophonous roar, you unleash a destructive wave of sound that washes over your enemies and passes around all cover except Total.
The Range of this Roar is a 15 foot Radial Area Sphere, striking all creatures on Land or Airborne. A creature within this area is forced to make a Constitution Saving Throw: DC equals 8 + CON + Proficiency.
On a failure, a creature takes 3d8 Thunder damage as the energy crashes into them. On a success, the creature takes half damage as it is able to resist your mighty bellow.
A creature made of inorganic material such as stone, crystal, or metal has disadvantage on this saving throw.

You can use this Action twice per Long Rest.

The Thunder Only Grows

The power within you grows even still. The fury of the Mountains, the quaking of the Earth, the shrieking of the Sky... These wild wills are your Zenith and now, you reach them.
The Mountains shall crumble before you, the Earth shall bend and kneel at the strike of your boot, the Sky shall split against your mighty roar. You are an Undeniable Cataclysm and this world will know you. When you walk, the World believes an Army is coming... Do not disappoint it.

You gain a slew of Class Feature improvements:

Thunderous Footfalls: The Radial Area of your Aura of difficult terrain and of your Action - Stomp both increase by 5 feet.

The Pounding Gale - Forceful Strikes: Your usages per turn increases from 1 to 2. Your Maximum uses of this Feature increases from 2 to 4, per Long Rest.

The Pounding Gale - Surging Steps: Your Maximum Movement Speed Bonus per turn from this feature, increases from 5 feet to 10 feet per turn.

Roar of the Howling Gods: Your Damage Dice rolled for this Feature increases from 3d8 up to 4d8.