tidykml demo (see comments for the data source and result)

sherman.r

library(dplyr)
library(ggmap)
library(ggplot2)
library(ggrepel)
# devtools::install_github("briatte/tidykml")
library(tidykml)

f <- system.file("extdata", "states.kml.zip", package = "tidykml")

p <- kml_polygons(f) %>%
  filter(name %in% c("Georgia", "South Carolina"))

m <- get_map(kml_bounds(p), source = "osm")

ggmap(m) +
  geom_polygon(data = filter(p, name == "Georgia"),
               aes(longitude, latitude, group = name, fill = "state"),
               alpha = 1/3, color = "white") +
  geom_line(data = kml_lines(f),
            aes(longitude, latitude),
            color = "white", size = 2) +
  geom_line(data = kml_lines(f),
            aes(longitude, latitude, lty = "march"), size = 1/2) +
  geom_point(data = kml_points(f),
             aes(longitude, latitude, color = "war"), alpha = 0.5, size = 6) +
  geom_label_repel(data = kml_points(f) %>%
                     mutate(year = gsub("(.*)(\\d{4})", "\\2", name)),
                   aes(longitude, latitude, label = year),
                   segment.color = NA, fill = "black", color = "white") +
  scale_linetype_manual("", values = c("march" = "solid"),
                     labels = "Sherman’s March, 1864") +
  scale_color_manual("", values = c("war" = "black"),
                     labels = "Major U.S. Civil War battle") +
  scale_fill_manual("", values = c("state" = "darkred"),
                     labels = "Confederate State of Georgia") +
  labs(title = "General Sherman’s March, November 15-December 21, 1864",
       subtitle = paste(
         "Sherman’s forces marched from Atlanta to Savannah,",
         "Georgia, implementing scorched earth policy along the way.")) +
  theme(
    axis.title = element_blank(),
    axis.ticks = element_blank(),
    axis.text = element_blank(),
    legend.box = "horizontal",
    legend.justification = c(0, 1),
    legend.key = element_blank(),
    legend.position = "top",
    legend.text = element_text(size = rel(1)),
    plot.caption = element_text(hjust = 0),
    plot.subtitle = element_text(size = rel(1)),
    plot.title = element_text(face = "bold")
    )

Data + inspiration – U.S. Civil War (Google My Maps)

Result