I read most of the replies in this thread, and I do agree that many of those issues contribute to a bad marriage - but, I don't think they are the starting point of a bad marriage.
Why do we get married? Do we meet someone say "oh gee, I think I could hate you, let's get married"? No, we meet someone and fall in love. Love conquers all; it is what keeps us from seeing some of those faults that we discover as the monotony of marital life sets in.
When the monotony of marriage sets in we get "comfortable" with each other. The more comfortable you are with someone, the more likely it is that you will feel more free to say things you wouldn't otherwise say. Imagine this: first date, the guy has a booger hanging from his nose. Most women would try to discretely signal this by wiping at their own nose, or even politely suggesting that your date use a kleenex. 5 years into marriage, your spouse has a booger hanging - how do we handle it? "You've got a booger in your nose, go blow it or something", and probably said with a tone that lacks the amount of politeness you would have used when the relationship was new. But, do bad marriages start with hanging boogers? No...
Bad marriages start with bad communication skills. At first we are careful in what we say, how we say it, and when we say it. We are mindful of the other person and their feelings. Once comfort sets in WE feel more comfortable with our feelings and not so hesitant about our spouse's feelings being hurt by off-hand (yet unintentionally hurtful) comments.
So, spouse gets told he has a booger in his nose and at the back of his mind an unformed question arises "why did she point that out so blatently at the dinner table with my mother sitting here?" Spouse doesn't voice anything about it because it's just an emotive response at this point. But then something else similar could happen and that voice gets stronger. By the time any deliberate realization happens, you've got full blown hurt feelings. He either locks it down, or it erupts into a fight. At which point the booger informing spouse goes "huh? What set you off, it was just a booger!!!"
Married people are going to fight. The difference is how they communicate during the fight. Push blame off on the other person, or voice their own feelings about how something has made them feel; Accept responsibility for their own failings or deny any culpability. And at the root of it all is having the tools to communicate effectively with each other. Any given concept which we want to express can be said in 100's of different ways - and all the fine nuances of language impact how our words are received and interpretted. Without understanding that, we can stick our foot in our mouths over and over until so much damage has been done that a couple can't see their way out of it, together.
If a married couple agreed to fine tune their communication methods and be willing to explain not only what they mean when they say something but how they interpret what the other person has said - they can make even the worst of situations survive (provided of course, they sincerely want them to survive). The fact is, none of us are really psychic. We rely on non-verbal clues to fill in the blanks in what our spouses say or don't say. We are also not perfect, which means we are going to misinterpret at least some of those clues (and in many cases we'll misinterpret a LOT of those clues). The only way to avoid that is to have really open communication with each other and to be willing to be honest about the intentions of what we say and reactions to what we hear. Most people don't really take the time to learn this about their spouses.
Two months before hubby and I were married, we started working on this skill. When he would say something that just didn't completely match his body language, I would tell him what I was noticing and ask if he really meant exactly what he said. He did the same with me. This forced both of us to really look at what we had said and if we were being honest in our words. It also helped us both learn to correctly interpret the non-verbal clues we give off. A couple of months into our marriage we had the first of 3 fights in our marriage. We had just moved into our house. We had boxes everywhere. I was in the dining room, he was in the kitchen. Like slow motion, I could see what he was getting ready to do. I was too far away to physically intervene so I did the only thing that came naturally, I yelled at him to stop. I mean YELLED. That raised his ire and he deliberately went ahead and did what he was getting ready to do. This took place in a matter of only three or four seconds. He had a stack of books in his hands and was getting ready to toss them in a box. I knew what was in the box, he didn't. Just a moment after he tossed the books, we heard the sound of shattering glass. We spent the next several hours in a frosty silence. That box had held a set of glass mixing bowls that my grandmother had received from her mother, and passed them on to me. Eventually we realized we had to talk to each other at some point in our lives. So we sat down and talked it out. I didn't place blame on him for breaking them; he hadn't known they were there. He didn't place blame on me for yelling because he realized it really had been the only way I could get his attention in time. We agreed that in the future, if I yelled at him he would stop and hear me out. I agreed that I would only raise my voice if there really were no other way to get his attention. We've stuck by that agreement the last 5 years and haven't had a single fight relating to that kind of issue since.
Good marriages start with effective communication, and bad marriages start with poor communication.
---edited because of typo---