Interpretation of a 2SLS Coefficient - Civil War Determinants
You have a model
$$(1)\  y = x \beta + e,$$
where $x$ is endogenous $\mathbb E[xe] \not =0$. This is the structural model in the sense that the parameter you are interested in is $\beta$ interpreted by its appearance in (1). In your case

y is civil conflict onset
x economic growth

suggesting that you are interested in examining how economic growth affects propensity for civil conflict. So positive $\beta$ means economic growth increase propensity for civil conflict.
Using 2SLS you get an IV-estimate of $\beta$ which we can denote $\hat \beta_{IV}$. When $\hat \beta_{IV}$ is positive it suggests that $\beta$ is positive and hence  economic growth increase propensity for civil conflict.
Interpretation is independent of $Cov(z,x)$ where $z$ is the instrument. Which in this case is

z is natural disaster.

For instrumental regression instruments must be relevant which in the simple univariate case reduces to $Cov(z,x) \not = 0$, but the sign is irrelevant (you can try to use $w := -z$ as instrument then $Cov(z,x) &lt; 0 \Leftrightarrow Cov(w,x) &gt; 0$ but the 2SLS estimate $\hat \beta_{IV}$ will be the same).