Old War

You have studied the tactics of old which have given you the skill to better use and exploit  defensive tactics in combat.

Shield Wall

Starting at 3rd level, you’re able to impose your shield between your enemies and allies.

First, You gain the protection fighting style: When a creature you can see attacks a target other than you that is within 5 feet of you, you can use your reaction to impose disadvantage on the attack roll. You must be wielding a shield.

Second, When a creature comes within 5 feet of you after moving at least 10 feet you can use your reaction to perform a shove attack to knock that creature prone. 

Phalanx

Beginning at 7th level, your defensive prowess allows you to block assaults that would devastate others.

Whenever you make a dexterity or strength saving throw, as a reaction you can add a +5 bonus to your saving throw total. 

Shield Break

At 10th level, Your understanding of guard stances have given you an edge when attacking through a hostile creature's defenses.

You can use your bonus action to reduce the AC of a hostile creature by 2 until the start of their next turn.

Aegis Protection

At 15th level, you attain the ability to shield nearby allies as well as yourself.

Any ally within 5 ft of you can add your constitution modifier to their AC.

Devastating Counter

Starting at 18th level, You have learn all there is about holding your enemies at bay.

When a hostile creature within 5 ft of you attacks or cast a spell at an allied creature(s). You can use your reaction to make one weapon attack against the attacker. If your roll total is 20 or more this attack cancels the hostile creature's attack or spell. Damage on hit is calculated normally. Once you use this feature you must finish a short rest before using it again.