I think the biggest threat to marriage comes from selecting the wrong mate.
Most people do very little if any introspective thinking to determine who they are, what they want, and what they need in a mate. Instead of approaching relationships from a point of "awareness" we tend to enter into relationships by "happenstance" or due to our physical attraction. Quite often people will move in together or get engaged before they know if they agree on major things. Each of us selects our own friends, lovers, and spouse. Therefore it's important to know if you are with someone who is "naturally" a great fit for you as opposed to someone who may be saying/doing what they think you want to "impress" you. Gradually they'll revert back to their natural self. It takes more time to get to know someone than most people are willing to invest. Other people decide to marry someone based upon circumstances or because they believe their mate has the "potential" to become what they "really" want in a spouse. More often than not it leads to frustration on their part and resentment on the part of their mate. "People change when they want to change."
"Trust" can only come after someone has demostrated honesty and integrity. You have to be given something to trust or distrust. Trusting "blindly" is a conman's dream! You have to allow others to "earn" your trust!
"Communication" is not "an ask and it shall be given proposition". Many folks confuse "communication" with "action". Communication is nothing more than one person expressing an idea or thought and having another person acknowledge they understood what was expressed. The best relationships are between those who "agree" on the major things in life. Opposites may attract in the short run but like attracts like in the long run! You have to know what YOU want before you merge your life with another!