Is there a way to make leather armor stronger?

Question

Is it possible to use a command to make leather armor stronger than diamond armor?

Making it harder to break?

Answer 1

This can only be done with a command block.

/give {name} minecraft:command_block

This will give the nearest player a Leather chestplate with the enchant Unbreaking level 32767 (max) (the Unbreaking enchantment ID is 34) and the lore (thing underneath) will say "May these protect you".

/give @p minecraft:leather_chestplate 1 0 {display:{Name:"PutNameHere",Lore:["May these protect you"]},ench:[{id:34s,lvl:32767s}]}

Answer 2

For this command, you will not need a command block, and this command will make the armor completely unbreakable. Here's the command:

/give @p minecraft:leather_chestplate 1 0 {Unbreakable:1}

Explained:

/give                          give
@p                             the nearest player
minecraft:leather_chestplate   a leather chestplate 
1                              one time  
0                              and make it have no damage  
{Unbreakable:1}                and make it unbreakable   

This will be resistant to anything when a player is wearing it, even though you will still be taking damage through it, and, sadly, the item will still be damageable (example: you can burn the item).