I thought a meme would be the best way to show my disagreement with your post. Plus hopefully someone laughs.

First, do we actually know this attack was made due to radical Islam? It could have been due to two crazy brothers who hate society and just happen to be chechen Muslims (are they even confirmed to be practicing Muslims?).

To answer the question question in the title, there are several things that need to be done. First and foremost, we need to stop supporting regimes, like those of Saudi Arabia and Qatar, that harbor radical ideologies. These regimes are the biggest reason for the spread of backwards ideologies like Wahabism, which is the ideology that most people are thinking of when it comes to radical Islam and terrorism. In fact Wahabism only really started spreading when Al Saud took power in Saudi Arabia. They helped spread it through oil money and continue to do so. Why do they and other gulf monarchies do that? Because these ideologies are tailored to keep tyrants in power. They were created by Ummayad and Abbasid (tyrants) "scholars" and some of their teachings include the requirement to follow the political leader, even if they are unjust. It is a long and painful history to talk about, so i won't get into it more than this.

Basically, these radical ideologies are harbored by the tyrants of the gulf, who also happen to be the west's biggest allies in the Muslim world. So if the west is serious about getting rid of Islamic radicalism, they need to stop supporting these regimes and allow the carpet to be ripped from under their feet. I have a feeling that will not happen anytime soon (look at Bahrain: most people do not know that there are constant anti government protests there). Of course, that does not mean the west should go invade these countires on a bunch of false premises to free them from the tyrants. Just stop supporting the regimes and they will fall by themselves eventually. Another idea is for the west to stop directly supporting radical militant groups just because they are useful pawns to fight against regimes that the west does not like. I am talking about groups like the "Free Syrian Army" here. They are terrorists, plain and simple. They should not be getting aid and weapons.

I also saw some people talking about how mainstream Muslims need to speak up and oppose these radicals. Do you not think that they already do that? How much do you think the average religious cleric and the average Muslim speak out against and condemn radical Islam and terrorism in Iraq, where I am originally from? Well we do it every day all year long. Does it stop the terrorist attacks that happen everyday? Clearly not. Me and the average person speaking out against it does not have enough power against money (oil money from the Gulf states usually) and a little bit of brainwashing on a poor teen or young adult. There will always be a few who fall for it, become radical, and become prone to carrying out attacks on innocent people.

We need better economies, more jobs, less radical clerics and regimes that support and harbor them (believe it or not there are Saudi clerics that openly call for the killing of and fighting against certain sects of Islam), and a bunch of other things to help keep the young happy, busy, practicing normal mainstream Islam, and away from radicalism.

The answer is radical christianism. They bomb each other till the world is religion free.

Accept Islam as the one true religion, stop putting whores on tv, keep electing Muslim presidents and establish sharia law as the law of the land. Or, we could ban violent video games, they probably learned their bombing skills from counter-strike

And it makes little sense to atttibute the attacks to "war on terror" until you fully know the motives and so on.  In short, it would be best for people to wait and see first.

HAHAHA!

GOLD!

When your YouTube playlist is full of jihadist videos and the people around you describe your religiosity as intensifying in recent years and you go out of the country for six months but no one knows where, then come back and blow up a public place... that is some pretty strong circumstantial evidence as to what the motive was.

Inequality creates a sense of alienation, alienation creates a sense of radicalization. Immigrants are especially sensitive to this, as Badgenome said. This does not mean that the wealthy do not become terrorists (most of the leaders of radicalized movements are often petite Bourgeouis or more), but the widespread cultural tendency towards radicalism is purely based on economic factors.

People around the suspect were shocked it happened.  They didn't see it coming, according to news reports.  I seriously suggest people wait before passing judgement on this.  

I can confirm that, at least in the Muslim countries, economic factors are very important. For example, in Iraq many people who plant road side bombs or the likes are young poor males who do it for like $50. The radicals or the violent political opposition simply pay them to do it or they recruit them with the promise of a better life. This is based on the confessions of many of them that I have seen on state television.