That's certainly an interesting question, friend, but I would respectfully point out it might be something of a loaded one. It's not necessarily true that Christianity and Islam have been "much more violent" than the religions you describe. While I'm sure our Asian specialists would be able to tell you more than I can, I would recommend checking out:

Brian Daizen Victoria, Zen At War (Rowman & Littlefield Publishers; 2nd edition, 2006)

Michael Jerryson and Mark Juergensmeyer, eds., Buddhist Warfare (Oxford University Press; 1 edition, 2010)

Both of these works describe how Buddhism has often been associated with war; Victoria’s book explores its role in Japanese militarism from the mid-19th century to the end of World War Two, and the essays in the collection take an even longer view, exploring Buddhism and bellicosity in various time periods over the centuries.

It’s also very difficult to say that these religions are less “powerful” than Christianity or Islam. One only needs to read a book on, say, Korea (Daniel Tudor’s Korea: The Impossible Country) or Viet Nam (Stanley Karnow’s history) to see how much these various faiths have influenced each other and how much they continue to influence much of Asia, a region with billions of people.

If you’re really looking for an answer, I would say what looks like the outsized success of Christianity and Islam comes from a variety of factors, such as an evangelistic impulse and also the role of colonization and globalization. Christian nations were able to secure footholds in the New World (that is to say, the Americas) and then spread across, spreading their religion to the Native Americans as well. The Atlantic slave trade brought many Africans to the Americas who would become Christian as well (though this process was quite complicated indeed; see Sylvia Frey’s Come Shouting to Zion), and one can’t discount plain old warfare; the Christianization of the Roman Empire and Arab expansion (as well as trade, missionary work, etc.) played a large role in the rise of both Christianity and Islam. But yes, as I imply above, much of the same could be said of Buddhism and Confucianism, and it’s difficult to argue they’re necessarily less successful than the Abrahamic faiths.

As /u/Gunlord500 points out, it's a loaded question, or at least grossly oversimplifying, to say that Christianity and Islam "have been much more violent". It's also assuming the fact that 'peacefulness' ought somehow to be correlated to 'becoming more powerful'.

For this question even to become a reasonable historical question, this is the methodology you'd need to work through:

1. Establishing a reasonable, and reasonably objective, standard and quanitification for what makes religions 'peaceable.'
2. Demonstrate that historically and with considerable continuity mainstream or dominant versions of both Islam and Chrisitanity have ranked relatively 'low' on that peace-scale, and that representative versions of the other three have rated 'high'.
3. Then you'd need to show some kind of other correlation of your peace-scale to power.
4. Only then would it make sense to ask what factors lead Islam and Christianity to be powerful "despite" being more violent.

Do you see how both difficult, and I would suggest, untenable, this question becomes as a line of historical inquiry?