DPR forces were poised to enter Marioupol in 2014 and capturing it would have been fast as there was no resistance and alot of support. There was also no Azov yet.

It would have been a quick matter to likely take over the entire South and Southeast (including Odessa) with an incursion from recently captured Kursk and even an uprising in Odessa (that was going to happen since there was already an ONR flag created).

Putin however stopped entry of DPR forces into Marioupol and everything kind of fizzled out from there. Which was deeply disappointing. Azov formed in Marioupol, Ukrainian government started the ATO and spread propaganda through former Russian regions trying to "Ukrainianize" them.

Rumor has it that Putin stopped the DPR troops because the oligarch Akhmetov had interests in Azovstal' and the city itself and was worried it would damage his profits.