A history degree is definitely one route to a career specializing in conflict/terrorism analysis. I'm taking US government jobs as an example: although you'd need to be a US citizen to apply for these, they're probably similar to opportunities and expectations in non-US or non-governmental counter-terrorism jobs. You can see a few current US job postings here.

This intelligence analysis position requires a bachelor's degree in Engineering, Foreign Area Studies, Geography, History, Imagery Science, International Affairs, Military Science, Physical Science, Political Science, Remote Sensing, or a related discipline. So history is definitely one of many options, but I think it's useful to dig a bit deeper into the qualifications a bit deeper. This job and this job both require experience:

performing research, analysis, production and dissemination of tasks relative to counterintelligence; counterterrorism; criminal; research, development and acquisition and/or cyber matters, identifying intelligence gaps, and developing and managing collection requirements.

The point is that you could get this experience in any number of fields. The key seems to be using your time in college to learn how to identify "intelligence gaps" – that is, developing a research question about crime or terrorism – and then doing the research, analyzing what you find, and synthesizing it into some sort of a product, like a senior thesis. With the emphasis on dissemination, you might consider writing a thesis that you could publish in a particular journal (not necessarily academic) or coming up with some other way to get your research "out there."

I'd take a close look at your college to see which research methods you like best. Anthropology and sociology are two other fields you might want to check out. Sample a few classes if you can, or meet with a few particular professors to see how they respond to your interests and whether they'll help you do a counterterrorism research project. Remember that their interests don't need to match yours perfectly. You might get a lot out of working with an early modern or medieval historian, for example, who could provoke you to approach contemporary problems from a new and innovative perspective.

Also, be sure you keep foreign languages in mind, especially since you'd like international employment. History programs tend to be good about supporting students who want to do research in foreign language sources. Anthropology departments can sometimes be better at supporting research in obscure language fields. I'm assuming that in addition to English you have Portuguese. Spanish or French would probably be an easy transition, or you could begin work in Arabic, Chinese, or whatever your college has strengths in.

An undergraduate history degree does not lock you into much, but it does not guarantee you much, either. It is a generalists' degree at the lower levels, ideally giving you skills useful in a variety of different areas of study and work (research, reading and writing non-fiction, synthetic and analytical thinking). To become a professor (of any sort) requires much more education (PhD).

Not knowing the differences between Brazil and the USA, I will say that it is not clear to me what "terrorism analyst" means in terms of career. Do you want to be an academic working in a policy school, writing papers (and maybe advising the government) on terrorism? If you are not enjoying IR then policy school may not be your cup of tea, but it should be noted there are many flavors of IR, political science, policy work, etc., and you might look into the others ones to figure out what your distaste is related to. (Some of these flavors are quantitative, some qualitative. Some are about theory, some are about empirical research. And so on.) History is a fine undergraduate degree for using as a stepping stone to this kind of graduate work (political science would be as well).

Do you want to work for a government, i.e. in an intelligence or defense agency? That no doubt has its own career path. I don't think a history degree would hurt you in this endeavor (again, undergraduate degrees topics, by themselves, don't matter so much these days in most cases, but your grades and university probably will), but you might be best seeking out someone (i.e. a recruiter) from the kind of agency you are interested in working for and talking to them about what kinds of career paths there are (i.e. whether some kind of masters' degree might be useful or necessary, as is sometimes the case).

My estimation is also that graduate training in the country you want to work in will probably make that international jump easier.

My generalized advice is to look around a bit and try to find people who actually do what you are interested in doing. Then look into their resumes — what kinds of degrees did they get, what kinds of educations (i.e. grad degrees) did they acquire, what was their path to getting where they ended up. I would not worry too much about what subject your undergraduate degree is in, because history will feed well into all of these interests (presuming you end up doing something relevant to them, like the history of terrorism or the history of a relevant region and time period — it will be a harder sell if you focus on, say, medieval Europe). Very few undergraduate degrees these days lead directly into non-entry-level jobs (engineering degrees, some financial degrees, some science degrees do), and history certainly doesn't feed into anything straightforward, but if you approach it as a set of skills and knowledge base it can be a very useful degree for a lot of different avenues, including (but not limited to) getting into graduate programs of the sort you will probably need for your interests.