一种方法（相当长的“整洁风格”管道，因此您可能希望将其分解以检查哪个执行哪个）：

library(tidyr)
library(lubridate)
library(zoo)

df |> ## df is a dataframe of the example data you provided
  mutate(across(ends_with('_date'),
                ~ as.Date(.x) |> as.yearmon()
                )
         ) |>
  group_by(conflict_id) |>
  summarize(start = min(start_date, na.rm = TRUE),
            end = max(end_date, na.rm = TRUE)
            ) |>
  rowwise() |>
  mutate(ym = seq(start, end, 1/12) |> list()) |>
  unnest_longer(ym) |>
  select(conflict_id, ym) |>
  group_by(conflict_id) |>
  mutate(year = year(ym),
         month = month(ym),
         duration = row_number(),
         termination = ifelse(duration < max(duration), 0, 1)
         )

+ # A tibble: 14 x 6
# Groups:   conflict_id [2]
   conflict_id ym         year month duration termination
         <int> <yearmon> <dbl> <dbl>    <int>       <dbl>
 1         100 Mai 1946   1946     5        1           0
 2         100 Jun 1946   1946     6        2           0
## ... lines removed
11         100 Mär 1947   1947     3       11           1
12         101 Mai 1950   1950     5        1           0
13         101 Jun 1950   1950     6        2           0
14         101 Jul 1950   1950     7        3           1
>